Methods and apparatus for treating a respiratory disorder

ABSTRACT

An oxygen concentrator  100  apparatus and a method thereof implement operations control to efficiently release oxygen enriched gas to reduce potential waste. The control methodology may include generating a profile such as a minimum inhalation flow profile of the user. The profile may be based on a size parameter of the user. The method may determine one or more control parameters characterizing a bolus of oxygen enriched gas based on the generated flow profile. The control methodology may then generate a bolus release control signal, such as for a supply valve, according to the determined one or more control parameters. The oxygen concentrator may then, with the control signal, release and deliver a bolus of oxygen enriched gas for a user such as for reducing waste.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/641,080, filed on Feb. 21, 2020, which is a national phase entryunder 35 U.S.C. § 371 of International Application No. PCT/AU2018/050904filed Aug. 24, 2018, published in English, which claims priority fromAustralian Provisional Application No. 2017903443, filed Aug. 25, 2017,the entire disclosure of which is incorporated herein by reference.

FIELD OF THE TECHNOLOGY

The present technology relates generally to methods and apparatus fortreating respiratory disorders, such as an oxygen concentrator. In someexamples, the technology more specifically concerns methods andapparatus for increasing the efficiency of an oxygen concentrator suchas with pulsed oxygen delivery.

DESCRIPTION OF THE RELATED ART

There are many users that require supplemental oxygen as part of LongTerm Oxygen Therapy (LTOT). Currently, the vast majority of users thatare receiving LTOT are diagnosed under the general category of ChronicObstructive Pulmonary Disease (COPD). This general diagnosis includessuch common diseases as Chronic Asthma, Emphysema, and several othercardio-pulmonary conditions. Other users may also require supplementaloxygen, for example, obese individuals to maintain elevated activitylevels, or infants with cystic fibrosis or broncho-pulmonary dysplasia.

Doctors may prescribe oxygen concentrators or portable tanks of medicaloxygen for these users. Usually a specific continuous oxygen flow rateis prescribed (e.g., 1 litre per minute (LPM), 2 LPM, 3 LPM, etc.).Experts in this field have also recognized that exercise for these usersprovides long term benefits that slow the progression of the disease,improve quality of life and extend user longevity. Most stationary formsof exercise like tread mills and stationary bicycles, however, are toostrenuous for these users. As a result, the need for mobility has longbeen recognized. Until recently, this mobility has been facilitated bythe use of small compressed oxygen tanks. The disadvantage of thesetanks is that they have a finite amount of oxygen and they are heavy,weighing about 50 pounds, when mounted on a cart with dolly wheels.

Oxygen concentrators have been in use for about 50 years to supply userssuffering from respiratory insufficiency with supplemental oxygen.Traditional oxygen concentrators used to provide these flow rates havebeen bulky and heavy making ordinary ambulatory activities with themdifficult and impractical. Recently, companies that manufacture largestationary home oxygen concentrators began developing portable oxygenconcentrators (POCs). The advantage of POCs is that they can produce atheoretically endless supply of oxygen. In order to make these devicessmall for mobility, the various systems necessary for the production ofoxygen enriched gas are condensed.

Portable oxygen concentrators seek to utilize their produced oxygen asefficiently as possible, in order to minimise weight, size, and powerconsumption. This may be achieved by delivering oxygen as a bolus timedto coincide with a detection of the start of user inspiration, in a modeknown as pulsed or demand (oxygen) delivery. This approach preservesaccumulated oxygen by minimizing or avoiding oxygen release during userexpiration.

There is therefore a need to improve pulsed oxygen delivery (POD) suchas to reduce waste of delivered oxygen for a given user. It may also bebeneficial if improvements to the device broadened its use for a largerrange of potential users, extending from adult to neonate.

SUMMARY

Methods and apparatus for treating a respiratory disorder as describedherein may be implemented with improved control of pulsed oxygendelivery, such as by controlling an electro-mechanical valve(s)governing oxygen enriched gas release from a storage vessel. Suchdevices may implement greater control over release of accumulated oxygenso as to permit beneficial oxygen delivery for the user while using lessoxygen by minimizing potential oxygen waste. Such improvement may occureven during user inspiration. For example, for a given user, a “deliveryenvelope” representing constraints for a release of oxygen over a timeperiod such as during a breath or inspiratory portion of breath, may beestimated based on certain user measurements and device settings. Thedelivery envelope may be defined as the region within which theparameters of the bolus may be set so as to eliminate retrograde flowwaste and/or anatomic deadspace waste of oxygen enriched gas for thatuser.

Furthermore, the bolus parameters may be varied within the deliveryenvelope so as to determine and deliver the optimal bolus parameters fora given user, i.e. those parameters that maximise the therapeutic effectof pulsed oxygen delivery for that user, or equivalently, minimisephysiologic deadspace waste. The determination may be subjective, basedon user feedback, and/or objective, based on sensor data.

Some versions of the present technology may include a method ofcontrolling oxygen enriched gas release with a controller of an oxygenconcentrator. The method may include generating a minimum inhalationflow profile of a user based on a size parameter of the user. The methodmay include determining one or more control parameters characterizing abolus of oxygen enriched gas based on the generated minimum inhalationflow profile. The method may include generating, with the controller, abolus release control signal for controlling release of a bolus ofoxygen enriched gas according to the determined one or more controlparameters.

In some versions, the method may further include calculating an alveolartime for the user based on the minimum inhalation flow profile, whereinthe one or more control parameters are further based on the calculatedalveolar time. The method may further include deriving a deliveryenvelope for the one or more control parameters from the minimuminhalation flow profile, and may further include constraining the one ormore control parameters within the delivery envelope. The method mayfurther include calculating an alveolar time for the user based on theminimum inhalation flow profile, wherein the delivery envelope may befurther based on the calculated alveolar time. The size parameter of theuser may be height such that the method may further include estimatingan anatomic deadspace of the user from the height, wherein the alveolartime may be further based on the estimated anatomic deadspace.

In some versions, the method may further include generating one or moresensor signals representing properties of the oxygen concentrator or theuser. The method may further estimating an inspiratory time of the userfrom the one or more sensor signals. The minimum inhalation flow profilemay be further based on the estimated inspiratory time. The method mayinclude determining a volume for the bolus based on a setting of theoxygen concentrator, wherein the one or more control parameters may befurther based on the determined volume for the bolus. The determiningthe volume for the bolus may be further based on a breathing rate of theuser. The method may further include estimating the breathing rate ofthe user from one or more sensor signals representing properties of theoxygen concentrator or the user. The determining the one or more controlparameters may include any or all of: setting an onset delay that may beless than an inspiratory time of the minimum inhalation flow profile;setting a bolus amplitude profile to correspond with the minimuminhalation flow profile between the onset delay and a bolus duration;and computing the bolus duration based on the bolus amplitude profileand the determined volume for the bolus. The determining the one or morecontrol parameters may include any or all of: setting an onset delaythat may be less than an inspiratory time of the minimum inhalation flowprofile; setting a bolus amplitude profile to be equal to a value of theminimum inhalation flow profile at the onset delay over a range from theonset delay to a bolus duration; and computing the bolus duration basedon the bolus amplitude profile and the determined volume for the bolus.

In some versions, the method may further include calculating an alveolartime for the user based on the minimum inhalation flow profile, whereinthe onset delay may be less than the calculated alveolar time. The sizeparameter may be a height of the user such that the method may furtherinclude estimating an anatomic deadspace of the user from the height ofthe user, wherein the calculated alveolar time may be further based onthe estimated anatomic deadspace. The determining the one or morecontrol parameters may include any or all of: setting a bolus durationthat may be less than an inspiratory time of the minimum inhalation flowprofile; setting a bolus amplitude profile to follow the minimuminhalation flow profile between an onset delay and the bolus duration;and computing the onset delay based on the bolus amplitude profile andthe determined volume for the bolus. The determining the one or morecontrol parameters may include any or all of: setting a bolus durationthat may be less than an inspiratory time of the minimum inhalation flowprofile; setting a bolus amplitude profile to be equal to a value of theminimum inhalation flow profile at an onset delay over a range from theonset delay to the bolus duration; and computing the onset delay basedon the bolus amplitude profile and the determined volume for the bolus.The method may further include calculating an alveolar time for the userbased on the minimum inhalation flow profile, wherein the bolus durationmay be less than the alveolar time. The size parameter may be a heightof the user such that the method may further include estimating ananatomic deadspace of the user from the height of the user, wherein thealveolar time may be further based on the anatomic deadspace.

In some versions, the method may further include any or all of:estimating a beneficial effect of a bolus delivered in accordance withthe bolus release control signal; determining one or more furthercontrol parameters characterizing an additional bolus of oxygen enrichedgas based on the minimum inhalation flow profile and the estimatedbeneficial effect; and generating, with the controller, a further bolusrelease control signal according to the determined one or more furthercontrol parameters.

In some versions, the method may further include receiving, in thecontroller, a boost signal from an input interface of the oxygenconcentrator, and in response thereto, controlling, by the controller ofthe oxygen concentrator, release of one or more boost boluses, wherein atotal volume of oxygen enriched gas of a released bolus of the one ormore boost boluses includes (1) an equivalent volume that satisfies acontinuous-flow-rate setting of the oxygen concentrator as set at theinput interface plus (2) an additional volume quantity of oxygenenriched gas. The controller may discontinue release of the additionalvolume quantity of oxygen enriched gas after a predetermined time or inresponse to a further signal from the input interface of the oxygenconcentrator. The determining the one or more control parameters mayinclude calculating the control parameters to reduce one or more ofretrograde flow waste, anatomic deadspace waste and physiologicdeadspace waste. The method may further include releasing a bolus ofoxygen enriched gas in accordance with the bolus release control signalfor delivery to the user via a delivery device, whereby the deliveredbolus reduces one or more of retrograde flow waste, anatomic deadspacewaste and physiologic deadspace waste.

Some versions of the present technology may include an oxygenconcentrator apparatus. The oxygen concentrator apparatus may include atleast two canisters. The oxygen concentrator apparatus may include gasseparation adsorbent disposed in the at least two canisters, wherein thegas separation adsorbent separates at least some nitrogen from air inthe at least two canisters to produce oxygen enriched gas. The oxygenconcentrator apparatus may include a compression system. The compressionsystem may include a compressor coupled to at least one of thecanisters, wherein the compressor compresses air during operation. Thecompression system may include a motor coupled to the compressor,wherein the motor drives operation of the compressor. The oxygenconcentrator apparatus may include an accumulator coupled to one or moreof the canisters, wherein oxygen enriched gas produced in one or more ofthe canisters may be passed into the accumulator during use. The oxygenconcentrator apparatus may include a controller, including one or moreprocessors, and a set of valves coupled to the controller. Thecontroller may be configured to control operation of the set of valvessuch as to (a) produce oxygen enriched gas into the accumulator and/or(b) release the produced oxygen enriched gas from the accumulator in atleast one bolus. The controller may be further configured to generate aminimum inhalation flow profile of a user based on a size parameter ofthe user. The controller may be further configured to determine one ormore control parameters characterizing the at least one bolus based onthe generated minimum inhalation flow profile. The controller may befurther configured to generate a bolus release control signal accordingto the determined one or more control parameters, the generated bolusrelease control signal configured to cause the at least one bolus to bereleased from the accumulator.

In some versions, the oxygen concentrator apparatus may further includea control panel coupled to the controller and configured to receive thesize parameter of the user via manual entry. The controller may includea carrier medium having processor control instructions that, whenexecuted by the one or more processors, cause the oxygen concentratorapparatus to perform any on the methods described herein.

Some versions of the present technology may include a method ofcontrolling oxygen enriched gas release with a controller of an oxygenconcentrator in pulsed oxygen delivery mode. The method may includederiving a delivery envelope of parameters of a potential bolus ofoxygen enriched gas based on a size parameter of a user. The method mayinclude determining one or more control parameters characterizing adeliverable bolus of oxygen enriched gas so that the one or more controlparameters may be constrained within the delivery envelope. The methodmay include generating, with the controller, a bolus release controlsignal for controlling release of a bolus of oxygen enriched gasaccording to the determined one or more control parameters. The methodmay further include calculating an alveolar time for the user based onthe size parameter, wherein the deriving the delivery envelope may befurther based on the calculated alveolar time. The method may furtherinclude generating a minimum inhalation flow profile for the user basedon the size parameter, wherein the deriving the delivery envelope may bebased on the minimum inhalation flow profile. The calculated alveolartime may be further based on the minimum inhalation flow profile. Thesize parameter of the user may be height such that the method mayfurther include estimating an anatomic deadspace of the user from theheight, wherein the calculated alveolar time may be further based on theestimated anatomic deadspace.

In some versions, the method may further include generating one or moresensor signals representing properties of the oxygen concentrator or theuser. The method may further include estimating an inspiratory time ofthe user from the one or more sensor signals. The derived deliveryenvelope may be further based on the estimated inspiratory time. Themethod may further may include determining a volume for the potentialbolus based on a setting of the oxygen concentrator, wherein the one ormore control parameters may be further based on the determined bolusvolume. The determining the bolus volume may be further based on abreathing rate of the user. The method may further include estimatingthe breathing rate of the user from one or more sensor signalsrepresenting properties of the oxygen concentrator or the user. Themethod may include any or all of estimating a beneficial effect of abolus delivered in accordance with the bolus release control signal;determining one or more further control parameters characterizing anadditional bolus of oxygen enriched gas based on the estimatedbeneficial effect, wherein the determined one or more further controlparameters are constrained within the delivery envelope; and generating,with the controller, a further bolus release control signal according tothe determined further control parameters.

In some versions, the method may include any or all of receiving, in thecontroller, a boost signal from an input interface of the oxygenconcentrator, and in response thereto, controlling, by the controller ofthe oxygen concentrator, release of one or more boost boluses, wherein atotal volume of oxygen enriched gas of a released boost bolus of the oneor more boost boluses may include (1) an equivalent volume thatsatisfies a continuous-flow-rate setting of the oxygen concentrator asset at the input interface plus (2) an additional volume quantity ofoxygen enriched gas. The controller may discontinue release of theadditional volume quantity of oxygen enriched gas after a predeterminedtime or in response to a further signal from the input interface of theoxygen concentrator.

In some versions, the determining the one or more control parameters mayinclude calculating the control parameters to reduce one or more ofretrograde flow waste, anatomic deadspace waste and physiologicdeadspace waste. The method may further include releasing a bolus ofoxygen enriched gas in accordance with the bolus release control signalfor delivery to the user via a delivery device, whereby the deliveredbolus may reduce one or more of retrograde flow waste, anatomicdeadspace waste and physiologic deadspace waste.

Some versions of the present technology may include an oxygenconcentrator apparatus. The apparatus may include at least twocanisters. The apparatus may include gas separation adsorbent disposedin the at least two canisters, wherein the gas separation adsorbentseparates at least some nitrogen from air in the at least two canistersto produce oxygen enriched gas. The apparatus may include a compressionsystem. The compression system may include a compressor coupled to atleast one of the canisters, wherein the compressor compresses air duringoperation. The compression system may include a motor coupled to thecompressor, wherein the motor drives operation of the compressor. Theapparatus may include an accumulator coupled to one or more of thecanisters, wherein oxygen enriched gas produced in one or more of thecanisters may be passed into the accumulator during use. The apparatusmay include a controller, including one or more processors. Theapparatus may include a set of valves coupled to the controller. Thecontroller may be configured to control operation of the set of valvesto (a) produce oxygen enriched gas into the accumulator and/or (b)release, such as in pulsed oxygen delivery mode, the produced oxygenenriched gas from the accumulator in at least one bolus. The controllermay be further configured to derive a delivery envelope of parameters ofa potential bolus of oxygen enriched gas based on a size parameter of auser. The controller may be further configured to determine one or morecontrol parameters characterizing a deliverable bolus of oxygen enrichedgas so that the one or more parameters are constrained within thedelivery envelope. The controller may be further configured to generatea bolus release control signal according to the determined one or morecontrol parameters. The bolus release control signal may be forcontrolling release of a bolus of oxygen enriched gas from theaccumulator.

In some versions, the apparatus may include a control panel coupled tothe controller. The controller may be configured to receive the sizeparameter of the user via manual entry on the control panel. Thecontroller may include a carrier medium having processor controlinstructions that, when executed by the one or more processors, causethe oxygen concentrator apparatus to perform any method describedherein.

Some versions of the present technology may include a method of aprocessor for generating an inhalation flow profile for a user. Themethod may include estimating a tidal volume for the user based on asize parameter of the user and a breathing rate of the user. The methodmay include generating the inhalation flow profile for the user from thetidal volume and an inspiratory time for the user. The size parametermay be height, such that estimating the tidal volume may includeestimating an alveolar minute ventilation for the user based on theheight of the user. Estimating the tidal volume may further includeestimating an anatomic deadspace for the user based on the height of theuser. Estimating the tidal volume may include adding the anatomicdeadspace to a ratio of the alveolar minute ventilation to the breathingrate of the user. Generating the inhalation flow profile may includecalculating a peak inspiratory flow rate for the user from the tidalvolume for the user, the inspiratory time, and a template function forthe inhalation flow profile. The template function may be a sinusoidalhalf-wave. The method further may include estimating the inspiratorytime from the size parameter. The method may further may include, with acontroller of a respiratory therapy device, controlling a respiratorytherapy based on the generated inhalation flow profile. The controllingthe respiratory therapy may include controlling an oxygen concentratorbased on the inhalation flow profile.

Some versions of the present technology may include an oxygenconcentrator apparatus. The oxygen concentrator may include at least twocanisters. The oxygen concentrator may include gas separation adsorbentdisposed in the at least two canisters. The gas separation adsorbentserves to separate at least some nitrogen from air in the at least twocanisters to produce oxygen enriched gas. The oxygen concentrator mayinclude a compression system. The compression system may include acompressor coupled to at least one of the canisters, wherein thecompressor compresses air during operation. The compression system mayinclude a motor coupled to the compressor, wherein the motor drivesoperation of the compressor. The oxygen concentrator may include anaccumulator coupled to one or more of the canisters, wherein oxygenenriched gas produced in one or more of the canisters may be passed intothe accumulator during use. The oxygen concentrator may include acontroller, including one or more processors. The oxygen concentratormay include a set of valves coupled to the controller. The controllermay be configured to control operation of the set of valves to (a)produce oxygen enriched gas into the accumulator and/or (b) release theproduced oxygen enriched gas from the accumulator. The controller may befurther configured to estimate a tidal volume for a user based on a sizeparameter of the user and a breathing rate of the user. The controllermay be further configured to generate an inhalation flow profile for theuser from the tidal volume and an inspiratory time for the user.

In some versions, the controller may include a carrier medium havingprocessor control instructions that, when executed by the one or moreprocessors, cause the oxygen concentrator apparatus to perform any ofthe methods described herein.

Some versions of the present technology may include a method of acontroller for controlling a respiratory therapy device. The method mayinclude estimating a resting energy expenditure of a user based on asize parameter of the user. The method may include estimating arespiratory parameter for the user based on the estimated resting energyexpenditure. The method may include controlling the respiratory therapydevice based on the estimated respiratory parameter.

In some versions, the respiratory parameter may be tidal volume suchthat the estimating the respiratory parameter may include any or all of:computing an alveolar minute ventilation based on the estimated restingenergy expenditure, and estimating a tidal volume based on the computedalveolar minute ventilation and a breathing rate for the user. Theestimating the tidal volume may account for an activity state of theuser to provide a minimum or elevated estimate of the tidal volume. Therespiratory therapy device may be a ventilator, wherein the estimatedtidal volume may be a minimum tidal volume estimate, and wherein thecontrolling the respiratory therapy device may include initialising lowtidal volume alarms based on the minimum tidal volume estimate. Therespiratory therapy device may be a ventilator, wherein the estimatedtidal volume may be an elevated tidal volume estimate, and wherein thecontrolling the respiratory therapy device may include initialising hightidal volume alarms based on the elevated tidal volume estimate. Therespiratory therapy device may be a ventilator, wherein the estimatedtidal volume may be a minimum tidal volume estimate, and wherein thecontrolling the respiratory therapy device may include initialising atidal volume for volume control modes based on the minimum tidal volumeestimate. The estimating the tidal volume may account for a pathology ofthe user to provide a typical estimate of the tidal volume for thepathology. The respiratory therapy device may be a ventilator, whereinthe estimated tidal volume may be a typical tidal volume estimate forthe pathology, and wherein the controlling the respiratory therapydevice may include initialising target tidal volume settings for volumeassurance modes using the typical tidal volume estimate.

In some versions, the respiratory parameter may be minute ventilationsuch that the estimating the minimum respiratory parameter may includeany or all of: computing an alveolar minute ventilation based on theresting energy expenditure, and estimating a minute ventilation based onthe computed alveolar minute ventilation and an estimate of an anatomicdeadspace for the user obtained from the size parameter. The estimatingthe minute ventilation may account for an activity state of the user toprovide a minimum or elevated estimate of the minute ventilation.

In some versions, the respiratory therapy device may be a ventilator,wherein the estimated minute ventilation may be a minimum minuteventilation estimate, and wherein the controlling the respiratorytherapy device may include initialising low minute ventilation alarmsbased on the minimum minute ventilation estimate. The respiratorytherapy device may be a ventilator, wherein the estimated minuteventilation may be an elevated minute ventilation estimate, and whereinthe controlling the respiratory therapy device may include initialisinghigh minute ventilation alarms based on the elevated minute ventilationestimate. The respiratory therapy device may be an oxygen concentratorsuch that the controlling the respiratory therapy device may include anyor all of: generating a minimum inhalation flow profile for the userfrom the estimated respiratory parameter; determining one or morecontrol parameters for a bolus of oxygen enriched gas produced by theoxygen concentrator based on the generated minimum inhalation flowprofile; and generating a bolus release control signal for controllingrelease of a bolus of oxygen enriched gas according to the determinedone or more control parameters.

Some versions of the present technology include a respiratory therapyapparatus. The apparatus may include a controller, including one or moreprocessors. The controller may be configured to control one or moreoperations of the respiratory therapy apparatus to produce a respiratorytherapy. The controller may be configured to estimate a resting energyexpenditure of a user based on a size parameter of the user. Thecontroller may be configured to estimate a respiratory parameter for theuser based on the estimated resting energy expenditure. The controllermay be configured to control an operation of the respiratory therapyapparatus based on the estimated respiratory parameter.

In some versions, the controller may include a carrier medium havingprocessor control instructions that, when executed by the one or moreprocessors, cause the respiratory therapy apparatus to perform any ofthe methods described herein.

Some versions of the present technology may include a method ofcontrolling oxygen enriched gas release with a controller of an oxygenconcentrator in pulsed oxygen delivery mode. The method may includedetermining one or more control parameters characterizing a deliverablebolus of oxygen enriched gas. The method may include generating, withthe controller, a bolus release control signal for controlling releaseof a bolus of oxygen enriched gas according to the determined one ormore control parameters. The method may include receiving, in thecontroller, a boost signal from an input interface of the oxygenconcentrator. The method may include, in response to the boost signal,controlling one or more further bolus release control signals forcontrolling release of one or more boost boluses, wherein a total volumeof oxygen enriched gas of a released bolus of the one or more boostboluses includes: (1) an equivalent volume that satisfies acontinuous-flow-rate setting of the oxygen concentrator as set at theinput interface plus (2) an additional volume quantity of oxygenenriched gas.

In some versions, the method may include discontinuing, by thecontroller, release of the additional volume quantity of oxygen enrichedgas after a predetermined time or in response to receiving, in thecontroller, a further signal from the input interface of the oxygenconcentrator.

Some versions of the present technology may include an oxygenconcentrator apparatus. The oxygen concentrator apparatus may include atleast two canisters. The oxygen concentrator apparatus may include gasseparation adsorbent disposed in the at least two canisters, wherein thegas separation adsorbent separates at least some nitrogen from air inthe at least two canisters to produce oxygen enriched gas. The oxygenconcentrator apparatus may include a compression system including acompressor coupled to at least one of the canisters, wherein thecompressor compresses air during operation; and a motor coupled to thecompressor, wherein the motor drives operation of the compressor. Theoxygen concentrator apparatus may include an accumulator coupled to oneor more of the canisters, wherein oxygen enriched gas produced in one ormore of the canisters may be passed into the accumulator during use. Theoxygen concentrator apparatus may include a controller, including one ormore processors, and a set of valves coupled to the controller. Thecontroller may be configured to control operation of the set of valvesto (a) produce oxygen enriched gas into the accumulator and/or (b)release the produced oxygen enriched gas from the accumulator. Thecontroller may be further configured to determine one or more controlparameters characterizing a deliverable bolus of oxygen enriched gas.The controller may be further configured to generate a bolus releasecontrol signal for controlling release of a bolus of oxygen enriched gasaccording to the determined one or more control parameters. Thecontroller may be further configured to receive a boost signal from aninput interface of the oxygen concentrator apparatus. The controller maybe further configured to, in response to the boost signal, control oneor more further bolus release control signals for controlling release ofone or more boost boluses, wherein a total volume of oxygen enriched gasof a released bolus of the one or more boost boluses includes: (1) anequivalent volume that satisfies a continuous-flow-rate setting of theoxygen concentrator apparatus as set at the input interface plus (2) anadditional volume quantity of oxygen enriched gas.

In some versions, the controller may be configured to discontinuerelease of the additional volume quantity of oxygen enriched gas after apredetermined time or in response to receiving a further signal from theinput interface of the oxygen concentrator apparatus.

The methods described herein can, in part, provide improved functioningin a controller or processor, such as of a controller or processor of aportable oxygen concentrator. Moreover, the methods/systems,devices/apparatus can provide improvements in the technological field ofautomated monitoring and/or treatment of respiratory disorders,including, for example, operations of portable oxygen concentrators.

Of course, portions of the aspects may form sub-aspects of the presenttechnology. Also, various ones of the sub-aspects and/or aspects may becombined in various manners and also constitute additional aspects orsub-aspects of the present technology.

Other features of the technology will be apparent from consideration ofthe information contained in the following detailed description,abstract, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present technology will become apparent to thoseskilled in the art with the benefit of the following detaileddescription of embodiments and upon reference to the accompanyingdrawings in which like reference numerals refer to similar elements:

FIG. 1 is a schematic diagram of the components of an example oxygenconcentrator;

FIG. 2 depicts a side view of the main components of an example oxygenconcentrator;

FIG. 3A depicts a perspective side view of an example compressionsystem;

FIG. 3B depicts a side view of an example compression system thatincludes a heat exchange conduit;

FIG. 4A is a schematic diagram of the outlet components of an oxygenconcentrator;

FIG. 4B depicts an outlet conduit for an oxygen concentrator;

FIG. 4C depicts an alternate outlet conduit for an oxygen concentrator;

FIG. 5 depicts an outer housing for an example oxygen concentrator;

FIG. 6 depicts an example control panel for an oxygen concentrator;

FIG. 7 is a graph illustrating various kinds of waste gas in pulsedoxygen delivery.

FIG. 8 is a flow chart illustrating a methodology that may beimplemented by a processor to estimate a bolus delivery envelope for auser.

FIG. 9 is a flow chart illustrating a methodology that may beimplemented by a processor to control delivery of a bolus within thebolus delivery envelope estimated using the method of FIG. 8 .

FIG. 10A is a graph illustrating a range of breathing rates for a rangeof heights from 50 to 180 centimetres derived from population age-ratedata.

FIG. 10B is a graph illustrating a range of inspiratory times for arange of breath periods from 0.5 to 10 seconds obtained from publishedclinical data.

FIG. 11 is a graph showing three representative volume capnograms(partial pressure of exhaled CO₂ plotted against exhaled volume) fromdifferent user groups.

While the technology may be implemented with various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and are described in detail herein. It should beunderstood, however, that the drawings and detailed description theretoare not intended to limit the technology to the particular formdisclosed. Various modifications, equivalents, and alternatives may beimplemented by combining any of the disclosed features of any of thespecific examples described.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present technology may be understood in accordance with theterminology used herein. Headings are for organizational purposes onlyand are not meant to be used to limit or interpret the description orclaims. As used in this specification and the appended claims, thesingular forms “a”, “an”, and “the” include singular and pluralreferents unless the content clearly dictates otherwise. Furthermore,the word “may” is used throughout this application in a permissive sense(i.e., having the potential to, being able to), not in a mandatory sense(i.e., must). The term “include,” and derivations thereof, mean“including, but not limited to.”

The term “coupled” as used herein means either a direct connection or anindirect connection (e.g., one or more intervening connections) betweenone or more objects or components. The phrase “connected” means a directconnection between objects or components such that the objects orcomponents are connected directly to each other. As used herein thephrase “obtaining” a device means that the device is either purchased orconstructed.

Oxygen concentrators take advantage of pressure swing adsorption (PSA).Pressure swing adsorption may involve using a compressor to increase gaspressure inside a canister that contains particles of a gas separationadsorbent. As the pressure increases, certain molecules in the gas maybecome adsorbed onto the gas separation adsorbent. Removal of a portionof the gas in the canister under the pressurized conditions allowsseparation of the non-adsorbed molecules from the adsorbed molecules.The gas separation adsorbent may be regenerated by reducing thepressure, which reverses the adsorption of molecules from the adsorbent.Further details regarding oxygen concentrators may be found, forexample, in U.S. Published Patent Application No. 2009-0065007,published Mar. 12, 2009, and entitled “Oxygen Concentrator Apparatus andMethod”, which is incorporated herein by reference.

Ambient air usually includes approximately 78% nitrogen and 21% oxygenwith the balance comprised of argon, carbon dioxide, water vapor andother trace gases. If a gas mixture such as air, for example, is passedunder pressure through a vessel containing a gas separation adsorbentbed that attracts nitrogen more strongly than it does oxygen, part orall of the nitrogen will stay in the bed, and the gas coming out of thevessel will be enriched in oxygen. When the bed reaches the end of itscapacity to adsorb nitrogen, it can be regenerated by reducing thepressure, thereby releasing the adsorbed nitrogen. It is then ready foranother cycle of producing oxygen enriched gas. By alternating canistersin a two-canister system, one canister can be collecting oxygen whilethe other canister is being purged (resulting in a continuous separationof the oxygen from the nitrogen). In this manner, oxygen can beaccumulated, such as in a storage container or other pressurizablevessel or conduit coupled to the canisters, from the ambient air for avariety of uses include providing supplemental oxygen to users.

As previously noted, delivery of the accumulated oxygen, such as from astorage container or accumulator, as a bolus timed to coincide with thestart of inspiration in a mode known as pulsed or demand (oxygen)delivery may help to conserve the produced/accumulated oxygen. Thisapproach, while avoiding the waste of delivering oxygen duringexpiration, still has the potential to waste oxygen, in at least thefollowing three ways:

(1) Any portion of the bolus whose flow rate exceeds the instantaneousinspiratory flow rate may not be inspired during the current breath. Forexample, some of this portion may flow back out of the user's nostrils(retrograde flow) to atmosphere, where it may pool around the airwayopening for subsequent inhalation, but more likely be wasted toatmosphere. Pooling of delivered oxygen may potentially occur within theuser's airways to be inhaled in the subsequent breath(s), such as duringmouth breathing, or if a bolus is delivered during the pause before thestart of inspiration. However, pooling is often unpredictable, so theconservative pulsed oxygen delivery assumption is that that any portionof a bolus whose flow rate exceeds the instantaneous inspiratory flowrate is wasted. This type of oxygen waste may be considered to be“retrograde flow waste.”

(2) Due to the nature of mammalian respiration—that of tidal breathingwith conduit airways to an internal lung—not all of the inspiratory flowreaches the gas-exchanging areas of the lung; the end portion of eachinspiration remains in the conduit airways (i.e., the anatomicdeadspace) and is exhaled without reaching the alveoli. Therefore,oxygen delivered during the later part of inspiration will only reachthe anatomic deadspace. This type of oxygen waste may be considered tobe “anatomic deadspace waste.”

(3) In COPD users, the lung can be relatively heterogeneous, in thatsome groups of alveoli are not perfused by blood and therefore form“physiologic deadspace”. Portions of the bolus that reach suchnon-functioning alveoli are also wasted. This type of oxygen waste maybe considered to be “physiologic deadspace waste.”

Examples of the present technology may be implemented to reduce orminimize any or all of these potential oxygen waste types.

For example, FIG. 1 illustrates a schematic diagram of an example oxygenconcentrator 100, that may be implemented with the present technology.Oxygen concentrator 100 may concentrate oxygen out of an air stream toprovide oxygen enriched gas to a user. As used herein, “oxygen enrichedgas” is composed of at least about 50% oxygen, at least about 60%oxygen, at least about 70% oxygen, at least about 80% oxygen, at leastabout 90% oxygen, at least about 95% oxygen, at least about 98% oxygen,or at least about 99% oxygen.

Oxygen concentrator 100 may be a portable oxygen concentrator. Forexample, oxygen concentrator 100 may have a weight and size that allowsthe oxygen concentrator to be readily carried or supported by handand/or in a carrying case, such as by a user of the oxygen concentrator.In one embodiment, oxygen concentrator 100 has a weight of less thanabout 20 lbs., less than about 15 lbs., less than about 10 lbs., or lessthan about 5 lbs. In an embodiment, oxygen concentrator 100 has a volumeof less than about 1000 cubic inches, less than about 750 cubic inches;less than about 500 cubic inches, less than about 250 cubic inches, orless than about 200 cubic inches.

Oxygen may be collected from ambient air by pressurising ambient air incanisters 302 and 304, which include a gas separation adsorbent. Gasseparation adsorbents useful in an oxygen concentrator are capable ofseparating at least nitrogen from an air stream to produce oxygenenriched gas. Examples of gas separation adsorbents include molecularsieves that are capable of separation of nitrogen from an air stream.Examples of adsorbents that may be used in an oxygen concentratorinclude, but are not limited to, zeolites (natural) or syntheticcrystalline aluminosilicates that separate nitrogen from oxygen in anair stream under elevated pressure. Examples of synthetic crystallinealuminosilicates that may be used include, but are not limited to:OXYSIV adsorbents available from UOP LLC, Des Plaines, IW; SYLOBEADadsorbents available from W. R. Grace & Co, Columbia, Md.; SILIPORITEadsorbents available from CECA S.A. of Paris, France; ZEOCHEM adsorbentsavailable from Zeochem AG, Uetikon, Switzerland; and AgLiLSX adsorbentavailable from Air Products and Chemicals, Inc., Allentown, Pa.

As shown in FIG. 1 , air may enter the oxygen concentrator through airinlet 106. Air may be drawn into air inlet 106 by compression system200. Compression system 200 may draw in air from the surroundings of theoxygen concentrator and compress the air, forcing the compressed airinto one or both canisters 302 and 304. In an embodiment, an inletmuffler 108 may be coupled to air inlet 106 to reduce sound produced byair being pulled into the oxygen concentrator by compression system 200.In an embodiment, inlet muffler 108 may be a moisture and soundabsorbing muffler. For example, a water absorbent material (such as apolymer water absorbent material or a zeolite material) may be used toboth remove or reduce water from the incoming air and to reduce thesound of the air passing into the air inlet 106.

Compression system 200 may include one or more compressors capable ofcompressing air. Pressurized air, produced by compression system 200,may be forced into one or both of the canisters 302 and 304. In someembodiments, the ambient air may be pressurized in the canisters to apressure approximately in a range of 13-20 pounds per square inch (psi).Other pressures may also be used, depending on the type of gasseparation adsorbent disposed in the canisters.

Coupled to each canister 302/304 are inlet valves 122/124 and outletvalves 132/134. As shown in FIG. 1 , inlet valve 122 is coupled tocanister 302 and inlet valve 124 is coupled to canister 304. Outletvalve 132 is coupled to canister 302 and outlet valve 134 is coupled tocanister 304. Inlet valves 122/124 are used to control or gate thepassage of air from compression system 200 to the respective canisters.Outlet valves 132/134 are used to release or gate gas from therespective canisters during a venting process. In some embodiments,inlet valves 122/124 and outlet valves 132/134 may be silicon plungersolenoid valves. Other types of valves, however, may be used. Plungervalves offer advantages over other kinds of valves by being quiet andhaving low slippage.

In some embodiments, a two-step valve actuation voltage may be used tocontrol inlet valves 122/124 and outlet valves 132/134. For example, ahigh voltage (e.g., 24 V) may be applied to an inlet valve to open theinlet valve. The voltage may then be reduced (e.g., to 7 V) to keep theinlet valve open. Using less voltage to keep a valve open may use lesspower (Power=Voltage*Current). This reduction in voltage minimizes heatbuildup and power consumption to extend run time from the battery. Whenthe power is cut off to the valve, it closes by spring action. In someembodiments, the voltage may be applied as a function of time that isnot necessarily a stepped response (e.g., a curved downward voltagebetween an initial 24 V and a final 7 V).

In an embodiment, pressurized air is sent into one of canisters 302 or304 while the other canister is being vented. For example, during use,inlet valve 122 is opened while inlet valve 124 is closed. Pressurizedair from compression system 200 is forced into canister 302, while beinginhibited from entering canister 304 by inlet valve 124. In anembodiment, a controller 400 is electrically coupled to valves 122, 124,132, and 134. Controller 400 includes one or more processors 410operable to execute program instructions stored in memory 420. Theprogram instructions are operable to perform various predefined methodsthat are used to control operation of the oxygen concentrator. Suchoperations are described in more detail herein. Thus, controller 400 mayinclude program instructions for controlling a generation of valvecontrol signals that control operations of the valves 122, 124, 132 and134. For example, controller 400 may include program instructions foroperating inlet valves 122 and 124 out of phase with each other, i.e.,when one of inlet valves 122 or 124 is opened, the other valve isclosed. During pressurization of canister 302, outlet valve 132 isclosed and outlet valve 134 is opened. Similar to the inlet valves,controller 400 may include program instructions for operating outletvalves 132 and 134 such that they are operated out of phase with eachother. In some embodiments, the voltages and the duration of thevoltages of the signals used to open the input and output valves may becontrolled by controller 400.

Check valves 142 and 144 are coupled to canisters 302 and 304,respectively. Check valves 142 and 144 are one-way valves that arepassively operated by the pressure differentials that occur as thecanisters are pressurized and vented. Check valves 142 and 144 arecoupled to canisters to allow oxygen produced during pressurization ofthe canister to flow out of the canister, and to inhibit back flow ofoxygen or any other gases into the canister. In this manner, checkvalves 142 and 144 act as one-way valves allowing oxygen enriched gas toexit the respective canister during pressurization.

The term “check valve”, as used herein, refers to a valve that allowsflow of a fluid (gas or liquid) in one direction and inhibits back flowof the fluid. Examples of check valves that are suitable for useinclude, but are not limited to: a ball check valve; a diaphragm checkvalve; a butterfly check valve; a swing check valve; a duckbill valve;and a lift check valve. Under pressure, nitrogen molecules in thepressurized ambient air are adsorbed by the gas separation adsorbent inthe pressurized canister. As the pressure increases, more nitrogen isadsorbed until the gas in the canister is enriched in oxygen. Thenonadsorbed gas molecules (mainly oxygen) flow out of the pressurizedcanister when the pressure reaches a point sufficient to overcome theresistance of the check valve coupled to the canister. In oneembodiment, the pressure drop of the check valve in the forwarddirection is less than 1 psi. The break pressure in the reversedirection is greater than 100 psi. It should be understood, however,that modification of one or more components would alter the operatingparameters of these valves. If the forward flow pressure is increased,there is, generally, a reduction in oxygen enriched gas production. Ifthe break pressure for reverse flow is reduced or set too low, there is,generally, a reduction in oxygen enriched gas pressure.

In an example embodiment, canister 302 is pressurized by compressed airproduced in compression system 200 and passed into canister 302. Duringpressurization of canister 302 inlet valve 122 is open, outlet valve 132is closed, inlet valve 124 is closed and outlet valve 134 is open.Outlet valve 134 is opened when outlet valve 132 is closed to allowsubstantially simultaneous venting of canister 304 while canister 302 ispressurized. Canister 302 is pressurized until the pressure in canisteris sufficient to open check valve 142. Oxygen enriched gas produced incanister 302 exits through check valve and, in one embodiment, iscollected in accumulator 109 that serves as a storage container.Optionally, oxygen enriched gas outlet from the accumulator 109 througha conduit to the user may optionally be controlled by an additionalvalve (not shown in FIG. 1 ). Such a valve may also be operated by thecontroller 400 (such as with control of program instructions) and itsoperations may be responsive to a sensor signal such as from one or moresignals from a sensor (not shown) such as a pressure or flow ratesensor.

After some period of time during pressurization, the gas separationadsorbent will become saturated with nitrogen and will be unable toseparate additional significant amounts of nitrogen from incoming air.This point is usually reached after a predetermined time of oxygenenriched gas production during a production cycle. In the embodimentdescribed above, when the gas separation adsorbent in canister 302reaches this saturation point, the inflow of compressed air is stopped(by inlet valve 122) and canister 302 is vented (by outlet valve 132) toremove nitrogen. During venting, inlet valve 122 is closed, and outletvalve 132 is opened. While canister 302 is being vented, canister 304 ispressurized to produce oxygen enriched gas in the same manner describedabove. Pressurization of canister 304 is achieved by closing outletvalve 134 and opening inlet valve 124. The oxygen enriched gas exitscanister 304 through check valve 144.

During venting of canister 302, outlet valve 132 is opened allowingpressurized gas (mainly nitrogen) to exit the canister throughconcentrator outlet 130. In an embodiment, the vented gases may bedirected through outlet muffler 133 to reduce the noise produced byreleasing the pressurized gas from the canister. As gas is released fromcanister 302, the pressure in the canister drops, allowing the nitrogento become desorbed from the gas separation adsorbent. The releasednitrogen exits the canister through outlet 130, resetting the canisterto a state that allows renewed separation of oxygen from an air stream.Outlet muffler 133 may include open cell foam (or another material) tomuffle the sound of the gas leaving the oxygen concentrator. In someembodiments, the combined muffling components/techniques for the inputof air and the output of gas, may provide for oxygen concentratoroperation at a sound level below 50 decibels.

During venting of the canisters, it is advantageous that at least amajority of the nitrogen is removed. In an embodiment, at least about50%, at least about 60%, at least about 70%, at least about 80%, atleast about 90%, at least about 95%, at least about 98%, orsubstantially all of the nitrogen in a canister is removed before thecanister is re-used in another cycle to separate oxygen from air. Insome embodiments, a canister may be further purged of nitrogen using anoxygen enriched stream that is introduced into the canister from theother canister.

In an example of such a purging process, a portion of the oxygenenriched gas may be transferred from canister 302 to canister 304 whencanister 304 is being vented of nitrogen. Transfer of oxygen enrichedgas from canister 302 to 304, during venting of canister 304, helps tofurther purge nitrogen (and other gases) from the canister. In anembodiment, oxygen enriched gas may travel through flow restrictors 151,153, and 155 between the two canisters. Flow restrictor 151 may be atrickle flow restrictor. Flow restrictor 151, for example, may be a0.009D flow restrictor (e.g., the flow restrictor has a radius 0.009″which is less than the diameter of the conduit or tube it is inside).Flow restrictors 153 and 155 may be 0.013D flow restrictors. Other flowrestrictor types and sizes are also contemplated and may be useddepending on the specific configuration and tubing or flow path used tocouple the canisters. In some embodiments, the flow restrictors may bepress fit flow restrictors that restrict air flow by introducing anarrower diameter in their respective tube or flow path. In someembodiments, the press fit flow restrictors may be made of sapphire,metal or plastic (other materials are also contemplated).

Flow of oxygen enriched gas is also controlled by use of valve 152 andvalve 154. Thus, the controller 400 may also include programinstructions for controlling a generation of valve control signals thatcontrol operations of the valves 152 and 154. For example, valves 152and 154 may be opened for a short duration during the venting process(and may be closed otherwise) to prevent excessive oxygen loss out ofthe purging canister. Other durations are also contemplated. In anexample, canister 302 is being vented and it is desirable to purgecanister 302 by passing a portion of the oxygen enriched gas beingproduced in canister 304 into canister 302. A portion of oxygen enrichedgas, upon pressurization of canister 304, will pass through flowrestrictor 151 into canister 302 during venting of canister 302.Additional oxygen enriched gas is passed into canister 302, fromcanister 304, through valve 154 and flow restrictor 155. Valve 152 mayremain closed during the transfer process, or may be opened ifadditional oxygen enriched gas is needed. The selection of appropriateflow restrictors 151 and 155, coupled with controlled opening of valve154 allows a controlled amount of oxygen enriched gas to be sent fromcanister 304 to 302. In an embodiment, the controlled amount of oxygenenriched gas is an amount sufficient to purge canister 302 and minimizethe loss of oxygen enriched gas through venting valve 132 of canister302. While this embodiment describes venting of canister 302, it shouldbe understood that the same process can be used to vent canister 304using flow restrictor 151, valve 152 and flow restrictor 153.

The pair of equalization/vent valves 152/154 work with flow restrictors153 and 155 to optimize the air flow balance between the two canisters.This may allow for better flow control for venting the canisters withoxygen enriched gas from the other of the canisters. It may also providebetter flow direction between the two canisters. It has been found that,while flow valves 152/154 may be operated as bi-directional valves, theflow rate through such valves varies depending on the direction of fluidflowing through the valve. For example, oxygen enriched gas flowing fromcanister 304 toward canister 302 has a flow rate faster through valve152 than the flow rate of oxygen enriched gas flowing from canister 302toward canister 304 through valve 152. If a single valve was to be used,eventually either too much or too little oxygen enriched gas would besent between the canisters and the canisters would, over time, begin toproduce different amounts of oxygen enriched gas. Use of opposing valvesand flow restrictors on parallel air pathways may equalize the flowpattern of the oxygen between the two canisters. Equalising the flow mayallow for a steady amount of oxygen available to the user over multiplecycles and also may allow a predictable volume of oxygen to purge theother of the canisters. In some embodiments, the air pathway may nothave restrictors but may instead have a valve with a built-in resistanceor the air pathway itself may have a narrow radius to provideresistance.

At times, oxygen concentrator may be shut down for a period of time.When an oxygen concentrator is shut down, the temperature inside thecanisters may drop as a result of the loss of adiabatic heat from thecompression system. As the temperature drops, the volume occupied by thegases inside the canisters will drop. Cooling of the canisters may leadto a negative pressure in the canisters. Valves (e.g., valves 122, 124,132, and 134) leading to and from the canisters are dynamically sealedrather than hermetically sealed. Thus, outside air may enter thecanisters after shutdown to accommodate the pressure differential. Whenoutside air enters the canisters, moisture from the outside air maycondense inside the canister as the air cools. Condensation of waterinside the canisters may lead to gradual degradation of the gasseparation adsorbents, steadily reducing ability of the gas separationadsorbents to produce oxygen enriched gas.

In an example, outside air may be inhibited from entering canistersafter the oxygen concentrator is shut down by pressurising bothcanisters prior to shutdown. For example, the controller 400 may controlsuch an operation in a shutdown process or shutdown sequence byoperating the compressor and controlling the valve(s) accordingly tocreate the pressurized condition. By storing the canisters under apositive pressure, the valves may be forced into a hermetically closedposition by the internal pressure of the air in the canisters. In anembodiment, the pressure in the canisters, at shutdown, should be atleast greater than ambient pressure. As used herein the term “ambientpressure” refers to the pressure of the surroundings in which the oxygenconcentrator is located (e.g. the pressure inside a room, outside, in aplane, etc.). In an embodiment, the pressure in the canisters, atshutdown, is at least greater than standard atmospheric pressure (i.e.,greater than 760 mmHg (Torr), 1 atm, 101,325 Pa). In an embodiment, thepressure in the canisters, at shutdown, is at least about 1.1 timesgreater than ambient pressure; is at least about 1.5 times greater thanambient pressure; or is at least about 2 times greater than ambientpressure.

In an embodiment, pressurization of the canisters may be achieved bydirecting pressurized air into each canister from the compression systemand closing valves, or the pertinent canister related valves, to trapthe pressurized air in the canisters. In an example, when a shutdownsequence is initiated, inlet valves 122 and 124 are opened and outletvalves 132 and 134 are closed. Because inlet valves 122 and 124 arejoined together by a common conduit, both canisters 302 and 304 maybecome pressurized as air and or oxygen enriched gas from one canistermay be transferred to the other canister. This situation may occur whenthe pathway between the compression system and the two inlet valvesallows such transfer. Because the oxygen concentrator operates in analternating pressurize/venting mode, at least one of the canistersshould be in a pressurized state at any given time. In an alternateembodiment, the pressure may be increased in each canister by operationof compression system 200. When inlet valves 122 and 124 are opened,pressure between canisters 302 and 304 will equalize, however, theequalized pressure in either canister may not be sufficient to inhibitair from entering the canisters during shutdown. In order to ensure thatair is inhibited from entering the canisters, compression system 200 maybe operated for a time sufficient to increase the pressure inside bothcanisters to a level at least greater than ambient pressure. Regardlessof the method of pressurization of the canisters, once the canisters arepressurized, inlet valves 122 and 124 are closed, trapping thepressurized air inside the canisters, which inhibits air from enteringthe canisters during the shutdown period. Achieving such a pressurizedcondition of the canisters may conclude the shutdown sequence. Such apressure condition may optionally be detected such as by using anoptional pressure sensor(s) in fluid communication with the canisters orconduits related thereto. Optionally, such a condition may be estimatedby a timed operation of the compression system for a predetermined timegiven known characteristics of the compression system and canisters.

Referring to FIG. 2 , an example oxygen concentrator 100 is depicted.Oxygen concentrator 100 includes a compression system 200, a canisterassembly 300, and a power supply 180 disposed within an outer housing170. Inlets 101 are located in outer housing 170 to allow air from theenvironment to enter oxygen concentrator 100. Inlets 101 may allow airto flow into the compartment to assist with cooling of the components inthe compartment. Power supply 180 provides a source of power for theoxygen concentrator 100. Compression system 200 draws air in through theinlet 106 and inlet muffler 108. Inlet muffler 108 may reduce noise ofair being drawn in by the compression system and also may include adesiccant material to remove water from the incoming air. Oxygenconcentrator 100 may further include a fan such as near the outlet 172used to vent air and other gases from the oxygen concentrator. An outletport 174 fluidly coupled to the accumulator may provide a connection(e.g., interference fit type connector) for coupling to a conduit ortube for gas delivery such as for a nasal cannula.

Compression System

In some embodiments, compression system 200 includes one or morecompressors. In another embodiment, compression system 200 includes asingle compressor, coupled to all of the canisters of canister system300. Turning to FIGS. 3A and 3B, an example compression system 200 isdepicted that includes compressor 210 and motor 220. Motor 220 iscoupled to compressor 210 and provides an operating force to thecompressor to operate the compression mechanism. For example, motor 220may be a motor providing a rotating component (e.g., an eccentricbearing) that causes cyclical motion of a component (e.g., a piston) ofthe compressor that compresses air. When compressor 210 is a piston typecompressor, motor 220 provides an operating force which causes thepiston of compressor 210 to be reciprocated. Reciprocation of the pistoncauses compressed air to be produced by compressor 210. The pressure ofthe compressed air is, in part, estimated by the speed at which thecompressor is operated (e.g., how fast the piston is reciprocated).Motor 220, therefore, may be a variable speed motor that is operable atvarious speeds to dynamically control the pressure of air produced bycompressor 210.

In one embodiment, compressor 210 includes a single head wobble typecompressor having a piston. Other types of compressors may be used suchas diaphragm compressors and other types of piston compressors. Motor220 may be a DC or AC motor and provides the operating power to thecompressing component of compressor 210. Motor 220, in an embodiment,may be a brushless DC motor. Motor 220 may be a variable speed motorcapable of operating the compressing component of compressor 210 atvariable speeds. Motor 220 may be coupled to controller 400, as depictedin FIG. 1 , which sends operating signals to the motor to control theoperation of the motor. For example, controller 400, such as inaccordance with program instructions of one or more processors of thecontroller, may send signals to motor 220 to: turn the motor on, turnmotor the off, and set the operating speed of motor.

Compression system 200 inherently creates substantial heat. Heat iscaused by the consumption of power by motor 220 and the conversion ofpower into mechanical motion. Compressor 210 generates heat due to theincreased resistance to movement of the compressor components by the airbeing compressed. Heat is also inherently generated due to adiabaticcompression of the air by compressor 210. Thus, the continualpressurization of air produces heat in the enclosure (e.g., housing170). Additionally, power supply 180 may produce heat as power issupplied to compression system 200. Furthermore, users of the oxygenconcentrator may operate the device in unconditioned environments (e.g.,outdoors) at potentially higher ambient temperatures than indoors, thusthe incoming air will already be in a heated state.

Heat produced inside oxygen concentrator 100 can be problematic. Lithiumion batteries are generally employed as a power source for oxygenconcentrators due to their long life and light weight. Lithium ionbattery packs, however, are dangerous at elevated temperatures andsafety controls are employed in oxygen concentrator 100 to shut down thesystem if dangerously high power supply temperatures are detected.Additionally, as the internal temperature of oxygen concentrator 100increases, the amount of oxygen generated by the concentrator maydecrease. This is due, in part, to the decreasing amount of oxygen in agiven volume of air at higher temperatures. If the amount of producedoxygen drops below a predetermined amount, the oxygen concentrator 100may automatically shut down, such as when a sensor detects the low levelof oxygen concentration in the produced gas.

Because of the compact nature of oxygen concentrators, dissipation ofheat can be difficult. Solutions typically involve the use of one ormore fans to create a flow of cooling air through the enclosure. Suchsolutions, however, require additional power from the power supply andthus shorten the portable usage time of the oxygen concentrator. In anembodiment, a passive cooling system may be used that takes advantage ofthe mechanical power produced by motor 220. Referring to FIGS. 3A and3B, compression system 200 includes motor 220 having an externalrotating armature 230. Specifically, armature 230 of motor 220 (e.g. aDC motor) is wrapped around the stationary field that is driving thearmature. Since motor 220 is a large contributor of heat to the overallsystem it is helpful to pull heat off of the motor and sweep it out ofthe enclosure. With the external high-speed rotation, the relativevelocity of the major component of the motor and the air in which itexists is very high. The surface area of the armature is larger ifexternally mounted than if it is internally mounted. Since the rate ofheat exchange is proportional to the surface area and the square of thevelocity, using a larger surface area armature mounted externallyincreases the ability of heat to be dissipated from motor 220. The gainin cooling efficiency by mounting the armature externally, allows theelimination of one or more cooling fans that are discrete from thecompression system motor, thus reducing the weight and power consumptionwhile maintaining the interior of the oxygen concentrator within theappropriate temperature range. Thus, additional motor(s) might not berequired such as for an addition fan. Additionally, the rotation of theexternally mounted armature creates movement of air proximate to themotor to promote additional cooling.

Moreover, an external rotating armature may help the efficiency of themotor, allowing less heat to be generated. A motor having an externalarmature operates similar to the way a flywheel works in an internalcombustion engine. When the motor is driving the compressor, theresistance to rotation is low at low pressures. When the pressure of thecompressed air is higher, the resistance to rotation of the motor ishigher. As a result, the motor does not maintain consistent idealrotational stability, but instead surges and slows down depending on thepressure demands of the compressor. This tendency of the motor to surgeand then slow down is inefficient and therefore generates heat. Use ofan external armature adds greater angular momentum to the motor whichhelps to compensate for the variable resistance experienced by themotor. Since the motor does not have to work as hard, the heat producedby the motor may be reduced.

In an embodiment, cooling efficiency may be further increased bycoupling an air transfer device 240 to external rotating armature 230.In an embodiment, air transfer device 240 is coupled to the externalarmature 230 such that rotation of the external armature causes the airtransfer device to create an airflow that passes over at least a portionof the motor. In an embodiment, air transfer device includes one or morefan blades 241, 243 coupled to the armature. In an embodiment, aplurality of fan blades may be arranged in an annular ring such that theair transfer device acts as an impeller 247 that is rotated by movementof the external rotating armature. As depicted in FIGS. 3A and 3B, airtransfer device 240 may be mounted to an outer surface of the externalarmature 230, in alignment with the motor. The mounting of the airtransfer device to the armature allows airflow to be directed toward themain portion of the external rotating armature, providing a coolingeffect during use. In an embodiment, the air transfer device directs airflow such that a majority of the external rotating armature is in theair flow path.

Further, referring to FIGS. 3A and 3B, air pressurized by compressor 210exits compressor 210 at compressor outlet 212. A compressor outletconduit 250 is coupled to compressor outlet 212 to transfer thecompressed air to canister system 300. As noted previously, compressionof air causes an increase in the temperature of the air. This increasein temperature can be detrimental to the efficiency of the oxygenconcentrator. In order to reduce the temperature of the pressurized air,compressor outlet conduit 250 is placed in the air flow path produced byair transfer device 240. At least a portion of compressor outlet conduit250 may be positioned proximate to motor 220. Thus, airflow, created byair transfer device, may contact both motor 220 and compressor outletconduit 250. In one embodiment, a majority of compressor outlet conduit250 is positioned proximate to motor 220. In an embodiment, thecompressor outlet conduit 250 is coiled around motor 220, as depicted inFIG. 3B. For example, the outlet conduit may spiral about the blades ofan impeller of the air transfer device. Gaps 251 may optionally beimplemented between the coils of the spiral to promote air movementbetween coils of the conduit 250 for improving the cooling efficiency.

In an embodiment, the compressor outlet conduit 250 is composed of aheat exchange metal. Heat exchange metals include, but are not limitedto, aluminum, carbon steel, stainless steel, titanium, copper,copper-nickel alloys or other alloys formed from combinations of thesemetals. Thus, compressor outlet conduit 250 can act as a heat exchangerto remove heat that is inherently caused by compression of the air. Byremoving heat from the compressed air, the number of molecules in agiven volume at a given pressure is increased. As a result, the amountof oxygen that can be generated by each canister during each pressureswing cycle may be increased.

The heat dissipation mechanisms described herein are either passive ormake use of elements required for the oxygen concentrator 100. Thus, forexample, dissipation of heat may be increased without using systems thatrequire additional power. By not requiring additional power, therun-time of the battery packs may be increased and the size and weightof the oxygen concentrator may be minimized. Likewise, use of anadditional box fan or cooling unit may be eliminated. Eliminating suchadditional features reduces the weight and power consumption of theoxygen concentrator.

As discussed above, adiabatic compression of air causes the airtemperature to increase. During venting of a canister in canister system300, the pressure of the gas being released from the canistersdecreases. The adiabatic decompression of the gas in the canister causesthe temperature of the gas to drop as it is vented. Thus, in someversions of the oxygen concentrator, the cooled vented gases fromcanister system 300 may be directed toward power supply 180 and/ortoward compression system 200 to utilize the temperature drop. In anexample, base 315 of canister system 300 receives the vented gases fromthe canisters. The vented gases 327 (e.g., nitrogen enriched, oxygendepleted air) are directed through one or more flow paths of the base315 toward outlet 325 of the base and toward power supply 180. Thevented gases, as noted, are cooled due to decompression of the gases andtherefore passively provide cooling to the power supply. When thecompression system is operated, the air transfer device will gather thecooled vented gases and direct the gases toward the motor of compressionsystem 200. Optional fan near outlet 172 may also assist in directingthe vented gas across compression system 200 and out of the housing 170.In this manner, additional cooling may be obtained without requiring anyfurther power requirements from the battery.

Outlet System

An outlet system, coupled to one or more of the canisters, includes oneor more conduits for providing oxygen enriched gas to a user. In anembodiment, oxygen enriched gas produced in either of canisters 302 and304 is collected in accumulator 109 through check valves 142 and 144,respectively, as depicted schematically in FIG. 1 . The oxygen enrichedgas leaving the canisters may be collected in an oxygen accumulator 109prior to being provided to a user. In some embodiments, a tube may becoupled to the accumulator 109, such as via the outlet port 174, toprovide the oxygen enriched gas to the user. Oxygen enriched gas may bedelivered to the user through an airway delivery device (e.g., conduitand cannula) that transfers the oxygen enriched gas to the user's mouthand/or nose. In an embodiment, an outlet may include a tube that directsthe oxygen toward a user's nose and/or mouth that may not be directlycoupled to the user's nose.

Turning to FIG. 4A, a schematic diagram of an embodiment of an outletsystem for an oxygen concentrator is shown. A supply valve 160 may becoupled to outlet tube to control the release of the oxygen enriched gasfrom accumulator 109 to the user. In an embodiment, supply valve 160 isan electromagnetically actuated plunger valve. Supply valve 160 isactuated by controller 400, by generating supply valve control signalsthat may be set according to control of the program instructions of thecontroller 400, to control the delivery of oxygen enriched gas to auser. Actuation of supply valve 160 typically is not timed orsynchronized to the pressure swing adsorption process. Instead,actuation may be synchronized to the user's breathing. Additionally,supply valve 160 may have continuously-valued or quantified actuation toenable provision of oxygen enriched gas according to a predeterminedamplitude profile as discussed in more detail herein. A proportionalvalve is an example of such a continuously-actuatable supply valve 160that may be implemented.

Oxygen enriched gas in accumulator 109 passes through supply valve 160into expansion chamber 162 as depicted in FIG. 4A. In an embodiment,expansion chamber 162 may include one or more devices that may beimplemented to determine an oxygen concentration of gas passing throughthe chamber. Oxygen enriched gas in expansion chamber 162 buildsbriefly, through release of gas from accumulator 109 by supply valve160, and then may be bled through a small orifice flow restrictor 175 toa flow rate sensor 185 and then to particulate filter 187. Flowrestrictor 175 may be a 0.025 D flow restrictor. Other flow restrictortypes and sizes may be used. In some embodiments, the diameter of theair pathway in the housing may be restricted to create restricted airflow. Flow rate sensor 185 may be any sensor capable of generating orinferring a signal representative of the rate of oxygen enriched gasflowing through the conduit. Particulate filter 187 may be used tofilter bacteria, dust, granule particles, etc. prior to delivery of theoxygen enriched gas to the user. The oxygen enriched gas passes throughfilter 187 to connector 190 which sends the oxygen enriched gas to theuser via conduit 192 and to pressure sensor 194. In some embodiments,pressure sensor 194 may generate a signal that is proportional to theamount of positive or negative pressure applied to a sensing surface.

The controller 400, in accordance with its program instructionsimplemented with the methodologies described in more detail herein, mayreceive the flow rate signal from the flow rate sensor 185 as a feedbacksignal to enable a closed-loop control of a continuously-valuedactuation of the supply valve 160. Such continuously-valued actuation ofthe supply valve 160 may control gas release in order to deliver a bolusof oxygen enriched gas according to a predetermined amplitude profile.Such controlled, continuously-valued actuation of supply valve 160 mayresult in a bolus of oxygen being provided at the correct time andaccording to an amplitude profile that assures rapid delivery into theuser's lungs with minimal retrograde flow waste and/or anatomicdeadspace waste. When the bolus can be delivered in this manner, theremay be a linear relationship between a prescribed continuous flow rateand a therapeutically equivalent bolus volume in pulsed delivery modefor a user at rest with a given breathing pattern. For example, thetotal volume of each bolus required to emulate a continuous-flowprescription may be equal to 11 mL (per bolus) for each LPM ofprescribed continuous flow rate, i.e., an 11 mL volume bolus for aprescription of 1 LPM; a 22 mL volume bolus for a prescription of 2 LPM;a 33 mL volume bolus for a prescription of 3 LPM; a 44 mL volume bolusfor a prescription of 4 LPM; a 55 mL volume bolus for a prescription of5 LPM; etc. This amount of the bolus volume (11 mL in this example) isreferred to as the LPM equivalent bolus volume. It should be understoodthat the LPM equivalent bolus volume may vary between oxygenconcentrators due to differences in construction design, tubing size,chamber size, etc. The LPM equivalent bolus volume will also varydepending on the user's breathing pattern.

Expansion chamber 162 may include one or more oxygen sensors that may beimplemented for determining an oxygen concentration of gas passingthrough the chamber. In an embodiment, the oxygen concentration of gaspassing through expansion chamber 162 is estimated using an oxygensensor 165. An oxygen sensor is a device capable of detecting oxygen ina gas. Examples of oxygen sensors include, but are not limited to,ultrasonic oxygen sensors, electrical oxygen sensors, and optical oxygensensors. In one embodiment, oxygen sensor 165 is an ultrasonic oxygensensor that includes an ultrasonic emitter 166 and an ultrasonicreceiver 168. In some embodiments, ultrasonic emitter 166 may includemultiple ultrasonic emitters and ultrasonic receiver 168 may includemultiple ultrasonic receivers. In embodiments having multipleemitters/receivers, the multiple ultrasonic emitters and multipleultrasonic receivers may be axially aligned (e.g., across the gasmixture flow path which may be perpendicular to the axial alignment).

The ultrasonic oxygen sensor in use, directs an ultrasonic sound wave(from emitter 166) through oxygen enriched gas disposed in chamber 162to receiver 168. Ultrasonic sensor assembly may be based on detectingthe speed of sound through the gas mixture to determine the compositionof the gas mixture (e.g., the speed of sound is different in nitrogenand oxygen). In a mixture of the two gases, the speed of sound throughthe mixture may be an intermediate value proportional to the relativeamounts of each gas in the mixture. In use, the sound at the receiver168 is slightly out of phase with the sound sent from emitter 166. Thisphase shift is due to the relatively slow velocity of sound through agas medium as compared with the relatively fast speed of the electronicpulse through wire. The phase shift, then, is proportional to thedistance between the emitter and the receiver and the speed of soundthrough the expansion chamber. The density of the gas in the chamberaffects the speed of sound through the chamber and the density isproportional to the ratio of oxygen to nitrogen in the chamber.Therefore, the phase shift can be used to measure the concentration ofoxygen in the expansion chamber. In this manner the relativeconcentration of oxygen in the accumulator 109 may be estimated as afunction of one or more properties of a detected sound wave travelingthrough expansion chamber 162.

In some embodiments, multiple emitters 166 and receivers 168 may beused. The readings from the emitters 166 and receivers 168 may beaveraged to cancel errors that may be inherent in turbulent flowsystems. In some embodiments, the presence of other gases may also bedetected by measuring the transit time and comparing the measuredtransit time to predetermined transit times for other gases and/ormixtures of gases.

The sensitivity of the ultrasonic sensor system may be increased byincreasing the distance between the emitter 166 and receiver 168, forexample to allow several sound wave cycles to occur between emitter 166and the receiver 168. In some embodiments, if at least two sound cyclesare present, the influence of structural changes of the transducer maybe reduced by measuring the phase shift relative to a fixed reference attwo points in time. If the earlier phase shift is subtracted from thelater phase shift, the shift caused by thermal expansion of expansionchamber 162 may be reduced or cancelled. The shift caused by a change ofthe distance between the emitter 166 and receiver 168 may beapproximately the same at the measuring intervals, whereas a changeowing to a change in oxygen concentration may be cumulative. In someembodiments, the shift measured at a later time may be multiplied by thenumber of intervening cycles and compared to the shift between twoadjacent cycles. Further details regarding sensing of oxygen in theexpansion chamber may be found, for example, in U.S. Published PatentApplication No. 2009-0065007, published Mar. 12, 2009, and entitled“Oxygen Concentrator Apparatus and Method, which is incorporated hereinby reference.

Flow rate sensor 185 may be used to determine the flow rate of oxygenenriched gas flowing through the outlet system. Flow rate sensors thatmay be used include, but are not limited to: diaphragm/bellows flowmeters; rotary flow meters (e.g. Hall effect flow meters); turbine flowmeters; orifice flow meters; and ultrasonic flow meters. Flow ratesensor 185 may be coupled to controller 400 to provide a flow ratesignal to the controller 400. The flow rate of gas flowing through theoutlet system may be an indication of the relative breathing volume ofthe user. Changes in the flow rate of gas flowing through the outletsystem may also be used to determine a breathing rate of the user.Controller 400 may control actuation of supply valve 160 based on thebreathing rate and/or breathing volume of the user, as estimated by flowrate sensor 185 by evaluation/processing of the flow rate signal at thecontroller 400.

In some embodiments, ultrasonic sensor system 165 and, for example, flowrate sensor 185 may provide a measurement of an actual amount of oxygenbeing provided. For example, flow rate sensor 185 may provide a signalto the controller 400 for the controller to determine a volume of gas(based on the flow rate signal) provided and ultrasonic sensor system165 may provide a signal to the controller 400 for the controller 400 todetermine the concentration of oxygen of the volume of gas provided.These two measurements together may be used by controller 400 todetermine an approximation of the actual amount of oxygen provided tothe user.

As previously mentioned, oxygen enriched gas passes through flow ratesensor 185 to filter 187. Filter 187 removes bacteria, dust, granuleparticles, etc. prior to providing the oxygen enriched gas to the user.The filtered oxygen enriched gas passes through filter 187 to optionalconnector 190. Connector 190 may be a “Y” connector coupling the outletof filter 187 to pressure sensor 194 and outlet conduit 192. Pressuresensor 194 may be implemented with the controller 400 to monitor thepressure of the gas passing through conduit 192 to the user. Changes inpressure sensed by pressure sensor 194 may be evaluated by thecontroller 400 to determine a breathing rate of a user, as well as theonset of inhalation (also referred to as the trigger instant).Controller 400 may control actuation of supply valve 160 based on thebreathing rate and/or onset of inhalation of the user, as estimatedusing pressure sensor 194 as described below. In an embodiment,controller 400 may control actuation of supply valve 160 based oninformation provided by flow rate sensor 185 and pressure sensor 194.

Oxygen enriched gas may be provided to a user through conduit 192, thatmay be coupled to the optional outlet port 174. In an embodiment,conduit 192 may be a silicone tube. Conduit 192 may be coupled to a userusing an airway delivery device 710, as depicted in FIGS. 4B and 4C.Airway delivery device 710 may be any device capable of providing theoxygen enriched gas to nasal cavities. Examples of airway deliverydevices include, but are not limited to: nasal masks, nasal pillows,nasal prongs, and nasal cannulas. A nasal cannula airway delivery deviceis depicted in FIG. 4B. During use, oxygen enriched gas from oxygenconcentrator 100 is provided to the user through conduit 192 and airwaycoupling member 710. Airway delivery device 710 is positioned proximateto a user's airway (e.g., proximate to the user's mouth and or nose) toallow delivery of the oxygen enriched gas to the user while allowing theuser to breathe air from the surroundings.

During use, oxygen enriched gas may be directed/released to airwaydelivery device 710 when a change in pressure is sensed proximate to theairway delivery device 710 by controller 400 detecting the pressurechange and controlling activating supply valve 160. In one embodiment,airway delivery device 710 may be coupled to a pressure sensor. When auser inhales air through their nose, the pressure sensor may detect theonset of inhalation as a drop in pressure proximate to the airwaydelivery device 710. Controller 400 of oxygen concentrator 100 mayprovide a bolus of oxygen enriched gas to the user at the onset ofinhalation.

In an alternate embodiment, a mouthpiece may be used to provide oxygenenriched gas to the user. As shown in FIG. 4C, a mouthpiece 720 may becoupled to oxygen concentrator 100. Mouthpiece 720 may be the onlydevice used to provide oxygen enriched gas to the user, or a mouthpiecemay be used in combination with a nasal airway delivery device (e.g., anasal cannula). As depicted in FIG. 4C, oxygen enriched gas may beprovided to a user through both a nasal airway delivery device 710 and amouthpiece 720.

Mouthpiece 720 is removably positionable in a user's mouth. In oneembodiment, mouthpiece 720 is removably couplable to one or more teethin a user's mouth. During use, oxygen enriched gas is directed into theuser's mouth via the mouthpiece. Mouthpiece 720 may be a night guardmouthpiece which is molded to conform to the user's teeth.Alternatively, mouthpiece may be a mandibular repositioning device. Inan embodiment, at least a majority of the mouthpiece is positioned in auser's mouth during use.

During use, oxygen enriched gas may be directed to mouthpiece 720 when achange in pressure is detected proximate to the mouthpiece 720. In oneembodiment, mouthpiece 720 may be coupled to a pressure sensor. When auser inhales air through their mouth, the pressure sensor may detect theonset of inhalation as a drop in pressure proximate to the mouthpiece720. Controller 400 of oxygen concentrator 100 may provide a bolus ofoxygen enriched gas to the user at the onset of inhalation.

During typical breathing of an individual, inhalation may occur throughthe nose, through the mouth or through both the nose and the mouth.Furthermore, breathing may change from one passageway to anotherdepending on a variety of factors. For example, during more activeactivities, a user may switch from breathing through their nose tobreathing through their mouth, or breathing through their mouth andnose. A system that relies on a single mode of delivery (either one ofnasal and oral but not both), may not function properly if breathingthrough the monitored pathway is stopped. For example, if a nasalcannula is used to provide oxygen enriched gas to the user, aninhalation sensor (e.g., a pressure sensor or flow rate sensor) may becoupled to the nasal cannula to determine the onset of inhalation. Ifthe user stops breathing through their nose, and switches to breathingthrough their mouth, the oxygen concentrator 100 may not know when toprovide the oxygen enriched gas since there is no pressure dropdetectable via the nasal cannula. Under such circumstances, oxygenconcentrator 100 may increase the flow rate and/or increase thefrequency of providing oxygen enriched gas until the inhalation sensordetects an inhalation by the user. If the user switches betweenbreathing modes often, the default mode of providing oxygen enriched gaswill cause the oxygen concentrator 100 to work harder, limiting theportable usage time of the system.

In an embodiment, a mouthpiece 720 is used in combination with an airwaydelivery device 710 (e.g., a nasal cannula) to provide oxygen enrichedgas to a user, as depicted in FIG. 4C. Both mouthpiece 720 and airwaydelivery device 710 are coupled to an inhalation sensor. In oneembodiment, mouthpiece 720 and airway delivery device 710 are coupled tothe same inhalation sensor. In an alternate embodiment, mouthpiece 720and airway delivery device 710 are coupled to different inhalationsensors. In either embodiment, the inhalation sensor(s) may detect theonset of inhalation from either the mouth or the nose. Oxygenconcentrator 100 may be configured to provide oxygen enriched gas to theparticular device (i.e. one of mouthpiece 720 and airway delivery device710) proximate to which the onset of inhalation was detected. Forexample, the flow path from the accumulator may split/branch to each ofthe mouthpiece and airway delivery device and each branch may have asupply valve controlled by controller 400. Alternatively, anelectromechanical three-way valve may be implemented as a supply valveand controlled by the controller 400 to selectively direct the bolus tothe desired branch of the flow path (i.e., one of the mouthpiece 720 andairway delivery device 710). Alternatively, oxygen enriched gas may beprovided to both mouthpiece 720 and the airway delivery device 710 ifonset of inhalation is detected proximate either device. The use of adual delivery system such as depicted in FIG. 4C may be particularlyuseful for users when they are sleeping and switch between nosebreathing and mouth breathing without conscious effort.

Controller System

Operation of oxygen concentrator 100 may be performed automaticallyusing an internal controller 400 coupled to various components of theoxygen concentrator 100, as described herein. Controller 400 includesone or more processors 410 and internal memory 420, as depicted in FIG.1 . Methodologies implemented to operate and monitor oxygen concentrator100 as described in more detail herein may be implemented by programinstructions stored in memory 420 or a carrier medium coupled tocontroller 400, and executed by one or more processors 410. A memorymedium may include any of various types of memory devices or storagedevices. The term “memory medium” is intended to include an installationmedium, e.g., a Compact Disc Read Only Memory (CD-ROM), floppy disks, ortape device; a computer system memory or random access memory such asDynamic Random Access Memory (DRAM), Double Data Rate Random AccessMemory (DDR RAM), Static Random Access Memory (SRAM), Extended Data OutRandom Access Memory (EDO RAM), Rambus Random Access Memory (RAM), etc.;or a non-volatile memory such as a magnetic media, e.g., a hard drive,or optical storage. The memory medium may comprise other types of memoryas well, or combinations thereof. In addition, the memory medium may belocated in a first computer in which the programs are executed, or maybe located in a second different computer that connects to the firstcomputer over a network, such as the Internet. In the latter instance,the second computer may provide program instructions to the firstcomputer for execution. The term “memory medium” may include two or morememory mediums that may reside in different locations, e.g., indifferent computers that are connected over a network.

In some embodiments, controller 400 includes one or more processor(s)410 that includes, for example, one or more field programmable gatearrays (FPGAs), microcontrollers, etc. included on a circuit boarddisposed in oxygen concentrator 100. Processor 410 is capable ofexecuting program instructions stored in memory 420. In someembodiments, program instructions may be built into processor 410 suchthat a memory external to the processor may not be separately accessed(i.e., the memory 420 may be internal to the processor 410).

Processor 410 may be electronically coupled (e.g., wired or wirelessly)to various components of oxygen concentrator 100, including, but notlimited to compression system 200, one or more of the valves used tocontrol fluid flow through the system (e.g., valves 122, 124, 132, 134,152, 154, 160), oxygen sensor 165, pressure sensor 194, flow rate sensor185, temperature sensors, fans, and any other component that may beelectrically controlled. In some embodiments, a separate processor(and/or memory) may be coupled to one or more of the components.

Controller 400 is programmed with program instructions as describedherein to operate oxygen concentrator 100 and is further programmed tomonitor the oxygen concentrator 100 for malfunction states. For example,in one embodiment, controller 400 is programmed to trigger an alarm ifthe system is operating and no breathing is detected by the user for apredetermined amount of time. For example, if controller 400 does notdetect a breath for a period of 75 seconds, an alarm LED may be litand/or an audible alarm may be sounded. If the user has truly stoppedbreathing, for example, during a sleep apnea episode, the alarm may besufficient to awaken the user, causing the user to resume breathing. Theaction of breathing may be sufficient for controller 400 to reset thisalarm function. Alternatively, if the system is accidently left on whenoutput conduit 192 is removed from the user, the alarm may serve as areminder for the user to turn oxygen concentrator 100 off.

Controller 400 is further coupled to oxygen sensor 165, and may beprogrammed for continuous or periodic monitoring of the oxygenconcentration of the oxygen enriched gas passing through expansionchamber 162. A minimum oxygen concentration threshold may be programmedinto controller 400, such that the controller lights an LED visual alarmand/or an audible alarm to warn the user of the low concentration ofoxygen.

Controller 400 is also coupled to internal power supply 180 and isconfigured to monitor the level of charge of the internal power supply.A minimum voltage and/or current threshold may be programmed intocontroller 400, such that the controller lights an LED visual alarmand/or an audible alarm to warn the user of low power condition. Thealarms may be activated intermittently and at an increasing frequency asthe battery approaches zero usable charge.

Further functions or methodologies of controller 400 are described indetail in other sections of this disclosure.

Outer Housing—Control Panel

FIG. 5 depicts an embodiment of an outer housing 170 of an oxygenconcentrator 100. In some embodiments, outer housing 170 may becomprised of a light-weight plastic. Outer housing includes compressionsystem inlets 106, cooling system passive inlet 101 and outlet 172 ateach end of outer housing 170, outlet port 174, and control panel 600.Inlet 101 and outlet 172 allow cooling air to enter the housing, flowthrough the housing, and exit the interior of housing 170 to aid incooling of the oxygen concentrator 100. Compression system inlets 106allow air to enter the compression system. Outlet port 174 is used toattach a conduit to provide oxygen enriched gas produced by the oxygenconcentrator 100 to a user.

Control panel 600 serves as an interface between a user and controller400 to allow the user to initiate predetermined operation modes of theoxygen concentrator 100 and to monitor the status of the system.Charging input port 605 may be disposed in control panel 600. FIG. 6depicts an example control panel 600.

In some embodiments, control panel 600 may include buttons to activatevarious operation modes for the oxygen concentrator 100. For example,control panel may include power button 610, dosage buttons 620, 622,624, 626, active mode button 630, sleep mode button 635, and a batterycheck button 650. In some embodiments, one or more of the buttons mayhave a respective LED that may illuminate when the respective button ispressed (and may power off when the respective button is pressed again).Power button 610 may power the system on or off. If the power button isactivated to turn the system off, controller 400 may initiate a shutdownsequence to place the system in a shutdown state (e.g., a state in whichboth canisters are pressurized as previously described). Dosage buttons620, 622, 624, and 626 allow the prescribed continuous flow rate ofoxygen enriched gas to be selected (e.g., 1 LPM by button 620, 2 LPM bybutton 622, 3 LPM by button 624, and 4 LPM by button 626). Such buttonsmay cause the oxygen concentrator 100 to deliver a rate of oxygen, whenin a pulsed or demand mode, at an LPM equivalent bolus volume thatcorresponds to the continuous rate selected as described herein.Altitude button 640 may be selected when a user is going to be in alocation at a higher elevation than the oxygen concentrator 100 isregularly used by the user.

Battery check button 650 initiates a battery check routine in the oxygenconcentrator 100 which results in a relative battery power remaining LED655 being illuminated on control panel 600.

A user may have a low breathing rate or depth if relatively inactive(e.g., asleep, sitting, etc.). The user may have a high breathing rateor depth if relatively active (e.g., walking, exercising, etc.). Anactive mode or an inactive mode may be activated automatically bycomparing the detected breathing rate or depth to a threshold.Additionally, or alternatively, the user may manually activate arespective active or inactive mode by pressing button 630 for activemode and button 635 for inactive (sleep) mode. The adjustments made bythe oxygen concentrator 100 in response to activating active mode orinactive mode are described in more detail herein.

Methods of Delivery of Oxygen Enriched Gas

The main use of an oxygen concentrator 100 is to provide supplementaloxygen to a user. Generally, the flow rate of supplemental oxygen to beprovided is estimated and prescribed by a physician. Typical prescribedcontinuous flow rates of supplemental oxygen may range from about 1 LPMto up to about 10 LPM. The most commonly prescribed continuous flowrates are 1 LPM, 2 LPM, 3 LPM, and 4 LPM.

In order to minimize the amount of oxygen enriched gas that is needed tobe produced while still emulating the effect of continuous flow at aprescribed continuous flow rate, controller 400 may be programmed tosynchronise delivery of the oxygen enriched gas with the user'sinhalations, a mode known as pulsed oxygen delivery (POD) or demandoxygen delivery. Releasing the oxygen enriched gas to the user only asthe user inhales may prevent unnecessary oxygen production (furtherreducing power requirements) by not releasing oxygen, for example, whenthe user is exhaling. Reducing the amount of oxygen produced mayeffectively reduce the amount of air compression needed for oxygenconcentrator 100 (and subsequently may reduce the power demand from thecompressors).

Oxygen enriched gas produced by oxygen concentrator 100 is stored in anoxygen accumulator 109 and released to the user as a bolus as the userinhales. The amount of oxygen enriched gas provided by the oxygenconcentrator 100 is controlled, in part, by supply valve 160. In anembodiment, supply valve 160 is opened to a sufficient degree and for asufficient amount of time to provide the appropriate amount of oxygenenriched gas, as estimated by controller 400, to the user.

In an embodiment, pressure sensor 194 may be implemented to determinethe onset of inhalation by the user. In use, a conduit 192 for providingoxygen enriched gas is coupled to a user's nose and/or mouth through theairway delivery device 710 and/or mouthpiece 720. At the onset of aninhalation, the user begins to draw air into their body through the noseand/or mouth. As the air is drawn in, a negative pressure is generatedat the end of the conduit, due, in part, to the venturi action of theair being drawn across the end of the delivery conduit. Controller 400may be configured to detect a drop in the pressure signal generated bythe pressure sensor 194, the drop indicating the onset of inhalation.Upon detection of the onset of inhalation, supply valve 160 is opened torelease a bolus of oxygen enriched gas from the accumulator 109,optionally after first waiting an interval known as the onset delay. Apositive change or rise in the pressure indicates an exhalation by theuser and is generally a time that release of oxygen enriched gas isdiscontinued. Generally, when the controller 400 detects a positivepressure change in the pressure signal generated by the pressure sensor194, valve 160 is closed until the next onset of inhalation.Alternatively, valve 160 may be closed by the controller 400 after apredetermined interval known as the bolus duration. By measuring theintervals between adjacent onsets of inhalation, the controller 400 mayestimate the user's breathing rate. By measuring the intervals betweenonsets of inhalation and the following onsets of exhalation, thecontroller 400 may estimate the user's inspiratory time.

The amount of the pressure change detected by pressure sensor 194 may beimplemented to refine the amount of oxygen enriched gas being providedto the user. For example, if a large negative pressure change isdetected by pressure sensor 194, the volume of oxygen enriched gasprovided/released to the user may be increased by the controller 400(through its dynamic control of a supply valve 160) to consider or takeinto account the increased volume of gas presumably being inhaled by theuser. If a smaller negative pressure change is detected, the volume ofoxygen enriched gas provided/released to the user may be decreased bythe controller 400 (through its dynamic control of a supply valve 160)to take into account the decreased volume of gas presumably beinginhaled by the user.

In some embodiments, the sensitivity of the pressure sensor 194 may beaffected by the physical distance of the pressure sensor 194 from theuser, especially if the pressure sensor is located in oxygenconcentrator 100 and the pressure difference is detected through theconduit 192 coupling the oxygen concentrator 100 to the user. In someembodiments, the pressure sensor 194 may be placed in the airwaydelivery device 710 used to provide the oxygen enriched gas to the user.A signal from the pressure sensor may be provided to controller 400 inthe oxygen concentrator 100 electronically via a wire or throughtelemetry such as through Bluetooth™ or other wireless technology.

A user breathing at a rate of 30 breaths per minute (BPM) during anactive state (e.g., walking, exercising, etc.) may consume two andone-half times as much oxygen as a user who is breathing at 12 BPMduring an inactive state (e.g., asleep, sitting, etc.). Pressure sensor194 may be implemented to determine the breathing rate of the user. Asdescribed above, controller 400 may process information received frompressure sensor 194 to determine a breathing rate based on the frequencyof the onset of inhalation. The detected breathing rate of the user maybe applied to adjust the bolus volume of oxygen enriched gas. The bolusvolume of the oxygen enriched gas may be increased, kept constant, ordecreased as the user's breathing rate increases, as specified by thedose rationing scheme/methodology employed by the oxygen concentrator100.

Additionally, controller 400 may automatically adjust the bolus volumebased on the activity mode of the oxygen concentrator 100.

In some embodiments, if the user's current breathing rate exceeds apredetermined threshold, controller 400 may implement an alarm (e.g.,visual and/or audio) to warn the user that the current breathing rate isexceeding the delivery capacity of the oxygen concentrator 100. Forexample, the threshold may be set at 40 breaths per minute.

In some embodiments, the sensitivity of the oxygen concentrator 100 topressure changes may be selectively attenuated to reduce false onset ofinhalation detections due to movement of air from a different source(e.g., movement of ambient air).

In some embodiments, in active mode, the sensitivity of the oxygenconcentrator 100 may be mechanically, electronically, orprogrammatically attenuated. For example, during active mode, controller400 may look for a greater pressure drop to indicate the start of a userbreath (e.g., an elevated threshold may be compared to the detectedpressure drop to determine if the bolus of oxygen should be released).In some embodiments, the pressure sensor 194 may be mechanically alteredto be less sensitive to pressure drops. In some embodiments, anelectronic signal from the pressure sensor may be electronically alteredto be less sensitive to small pressure drops. In some embodiments,during the inactive mode, the sensitivity of the oxygen concentrator 100may be increased. For example, the controller 400 may look for a smallerpressure drop to indicate the onset of inhalation (e.g., a smallerthreshold may be compared to the detected pressure drop to determine ifthe bolus of oxygen should be released).

Tailoring POD Therapy to a User

In one implementation of pulsed oxygen delivery (POD) therapy ascontrolled by the methodology of the controller 400, the bolus can betailored to match the needs of a particular user. The objective may befor an oxygen bolus optimised to the user's breathing pattern, or tomaximize alveolar delivery, or both. To do so, an inhalation flowprofile may be determined and generated based on information gatheredfrom pressure sensor 194 and/or flow rate sensor 185. An inhalation flowprofile is determined/generated based on one or more of the followingparameters: the breathing rate of the user; the inhalation volume of theuser; the exhalation volume of the user; the peak inspiratory flow rateof the user; and the peak expiratory flow rate of the user. Thebreathing rate of the user may be estimated by detecting the onsets ofinhalation using pressure sensor 194 as previously discussed. Inhalationvolume may be estimated by measuring the change in pressure duringinhalation (absent any bolus) and calculating or empirically estimatingthe inhalation volume based on the change in pressure. Exhalation volumemay be estimated in a similar manner using positive pressure changesduring exhalation. Detection of the end of inhalation may be from thepressure sensor 194. When onset of inhalation is detected using thepressure sensor 194, the onset is characterized by a drop in pressure,relative to ambient. When the pressure begins to increase above ambient,the inhalation is considered complete.

There is a minimum rate of gas exchange necessary to sustain a typicalperson, which can be expressed as a minimum minute ventilation (e.g., aminimum volume of gas inspired and expired in the course of a minute).Assuming ventilation remains at this minimum minute ventilation, aperson who is breathing rapidly is inhaling a lower volume of air ineach breath and vice-versa. Hence a minimum tidal volume can beestablished from the minimum minute ventilation with additionalknowledge of breathing rate. By measuring a large population of users, ageneric profile of the relative inspiratory flow rate from onset ofinhalation to the onset of exhalation may be established/determined.Using the minimum tidal volume and the breathing rate, this genericrelative flow rate profile may be adapted mathematically into a minimuminhalation flow profile for a user. This minimum inhalation flow profile(e.g., an inspiratory flow rate versus time representation, such as indata or digital form, that may have a particular shape or curve duringinspiration time) can serve as a basis for control parameters thatcontrol actuation of a supply valve 160 to release, for delivery, anappropriate or corresponding bolus for the user.

Inhalation flow profile data empirically gathered from a population ofusers may be evaluated by or used to create an algorithm that determinesthe appropriate bolus (e.g., volume and shape) based on the estimatedminimum inhalation flow profile.

Basing the delivery of oxygen enriched gas on population data andbreathing rate might not take into account differences betweenindividual users. For example, people having similar breathing rates canhave different inhalation/exhalation volumes, inhalation/exhalation flowrates and, thus, different bolus parameters necessary to produce anappropriate bolus that would more closely correspond to a particularuser. A more accurately estimated inhalation flow profile of the usermay provide a more accurate basis for control of the bolus of oxygenenriched gas being provided to the user.

Estimating a Delivery Envelope for a User

FIG. 7 contains a graph 700 illustrating various kinds of waste in POD.The graph 700 contains two traces: trace 715, which represents therespiratory flow rate for a person's breath (positive indicatesinspiration) such as determined by a flow rate sensor, and trace 725,which represents respiratory effort (muscular pressure, with negativevalues indicating inspiratory effort) such as determined by arespiratory effort chest strap type sensor. The interval 745 representsthe inspiratory time. The trace 730 represents the amplitude profile ofa rectangular bolus of delivered oxygen. (Note that hereinafter, theterm “oxygen” is used as shorthand for “oxygen enriched gas”, unless itsalternative meaning of pure O₂ gas is clear from the context.) Theparameters of the rectangular bolus are its amplitude 735, its onsetdelay 740 from the onset of inhalation, and its duration 750. A moregeneral (e.g., non-rectangular) bolus may have a non-constant amplitudeprofile (amplitude over time), including a profile controlled to matchor correspond with an estimate of the user's inhalation flow profile.

The hatched area 760 represents the retrograde flow waste portion of thebolus, i.e. the portion of the bolus whose flow rate exceeds theinspiratory flow rate. The interval 770 represents the “alveolar time”T_(ALV) of the breath, i.e. the interval during which inhaled airreaches the gas-exchanging portion of the lung. After the interval 770,inspired flow only reaches the anatomic deadspace. Any portion of thebolus that lasts beyond the alveolar time T_(ALV) is therefore wasted onanatomic deadspace (anatomic deadspace waste).

For a user with COPD, some portion of the inspired air during thealveolar time T_(ALV), and therefore some portion of the bolus, may alsobe wasted because it does not reach functioning alveoli. This kind ofwaste (physiologic deadspace waste) is not illustrated in FIG. 7 .

It may be observed from FIG. 7 that the three parameters of a bolus,namely its onset delay, its duration, and its amplitude profile, mayvary within certain ranges without incurring retrograde flow or anatomicdeadspace waste for a given bolus volume. However, these ranges ofvariation are interdependent. For example, when a shorter onset delay ischosen, the upper bound on amplitude will need to be lower so that thebolus amplitude profile remains within the area of the user'srespiratory flow rate curve that avoids retrograde flow waste oranatomic deadspace waste. Furthermore, for a bolus of predeterminedvolume, once the amplitude profile is chosen, the duration is fixedalso, and vice versa. The interdependence of these parameters, which mayserve as control parameters for release of a bolus, may be expressed ina “delivery envelope”, a region in parameter space within which thebolus control parameters may be constrained so that the bolus maydelivered without incurring retrograde flow waste or anatomic deadspacewaste.

The volume of anatomic dead space can be estimated, for example,according to user height or some surrogate dimension (e.g. ulna length,knee-heel distance, etc.). Given this value and the user's estimatedinhalation flow profile as previously described, the user's alveolartime T_(ALV) may be estimated, and this value along with the inhalationflow profile itself would provide the interdependent limits on onsetdelay and amplitude profile for the control of bolus release/generation.The difficulty in estimating the delivery envelope is that a givenuser's inhalation flow profile is unknown. Although pressure sensor 194can in theory be calibrated to adequately measure the instantaneousrespiratory flow rate (absent any bolus), in practice such calibrationcannot be relied upon during POC therapy because (a) during delivery ofthe bolus the nasal pressure signal is lost, and (b) change in cannulaposition is routine, so any ‘calibration’ of a signal from pressuresensor 194 against respiratory flow rate is at best temporary.

However, to estimate a delivery envelope, the user's actual inhalationflow profile is not required. Instead, a ‘worst case’ might beconservatively assumed, which for pulsed oxygen delivery is that ofminimum ventilatory demand for a given user size. On this assumption,anatomic deadspace is maintained while tidal volume is reduced, which isworst case for delivery of the oxygen bolus due to the followingconspiring effects:

(a) a longer onset delay (740) due to low inspiratory flows;

(b) the anatomic deadspace occupies an increased proportion of theinspiratory time, such that alveolar time (interval 770) is reduced, and

(c) the inhalation flow profile is shallow so the bolus amplitude mustbe small to avoid retrograde flow waste (area 760).

In overview, a minimum alveolar ventilation may be inferred from aparameter representing the user's body size, e.g. height. Knowing userheight also permits estimation of the particular volume portion of thebreath that fills the anatomic deadspace. A minimum tidal volume canthus be calculated using the measured breathing rate. Inspiratoryduration can be measured as described above, or estimated from thebreathing rate, which combined with the minimum tidal volume and ageneric relative inhalation profile allows estimation of a minimuminhalation flow profile, i.e. the minimum instantaneous flow ratethroughout inspiration. While body size is a preferred user parameterfor this purpose, other user parameters may offer similar (but lessspecific) inference, such as age, weight, sex or combinations thereof.In particular, the use of body size to infer a minimum inhalation flowprofile allows the range of users to extend from adult to neonate.

FIG. 8 contains a flow chart illustrating a method 800 that may beimplemented to estimate the delivery envelope. The method 800 may beimplemented by the controller 400, appropriately configured by programinstructions stored in memory 420 or a carrier (storage) medium coupledto controller 400, and executed by one or more processors 410 asdescribed above.

The controller 400 may be configured to perform the method 800 only oncefor a user. Alternatively, the method 800 may be performed repeatedly,for example once per breath, to account for changes in the user'sbreathing rate and inspiratory time, since these changes will affect thedelivery envelope.

The principles underlying the method 800 are:

1. Estimation of the user's anatomic deadspace: Anatomic dead space isapproximately correlated to a person's height, and effectively imposes aper-breath augmentation of tidal volume. The method 800 therefore maystart at step 810, which estimates the user's anatomic deadspaceVD_(an). The estimate may be based on their height. For example, afunction may apply a value of height to calculate a value for anatomicdeadspace volume or a look-up table may be accessed with the heightvalue to select a corresponding value for anatomic deadspace volume. Theuser's height (H) may be manually entered/input to the oxygenconcentrator 100 via its control panel 600, stored in the memory 420,and accessed by the controller 400. In one implementation, step 810 mayimplement the formula:

VD _(an)=7.585×10⁻⁴ ×H(cm)^(2.363)  (1)

Optionally, a known/measured anatomic deadspace may instead beused/input when available.

2. Estimation of minimum sustainable alveolar ventilation: Mammalspossess a minimum resting energy expenditure, also called basalmetabolic rate, and in the case of human beings this quantity can beloosely estimated from a person's height (or length for infants). Theassociated metabolism produces a minimum volume of CO₂, i.e. demands aminimum alveolar ventilation. Step 820 therefore makes use of the user'sheight to estimate the user's minimum alveolar minute ventilation suchas by calculation with a function or by look-up table. In oneimplementation, the user's resting energy expenditure (REE) is estimatedfrom the user's height, and the REE is used to estimate the user'sminimum alveolar minute ventilation, V^(&) _(ALV(min)).

In one implementation, the user's REE may be estimated from the user'sheight (e.g., in centimetres) as a piecewise linear interpolationbetween four breakpoints: H=40, 90, 140, and 190 cm. The correspondingREE values (e.g., in Megajoules per day) at each height breakpoint areas follows:

REE(40 cm)=0.11

REE(90 cm)=3.14

REE(140 cm)=4.82

REE(190 cm)=7.35  (2)

In other implementations, alternative estimates for REE may be madebased on other user parameters such as age, weight, and/or sex.

In one implementation, the user's minimum alveolar minute ventilation,V^(&) _(ALV(min)) (e.g., in litres per minute) may be estimated from theuser's resting energy expenditure (REE) as follows:

$\begin{matrix}{{V\&}_{{ALV}(\min)} = {{REE} \times 29.1 \times {Activity}{Factor} \times \left( \frac{P_{amb} - {47{mm}{Hg}}}{PACO_{2}} \right)}} & (3)\end{matrix}$

where PACO₂ is the arterial pressure of CO₂ in the bloodstream(typically 40 mmHg, but can range as high as 60 mmHg for hypercapnicusers), P_(amb) is the ambient pressure (typically 760 mmHg at sealevel, with a precise value determined in some implementations bysensing using an ambient pressure sensor on the oxygen concentrator100). ActivityFactor is an activity factor whose minimum value is unity(one), which when used will give minimum estimates for the user'srespiratory parameters such as alveolar minute ventilation, tidalvolume, and inhalation flow profile.

The activity factor may be applied to derive different inhalation flowprofiles so as to permit its variation in relation to a characterizationof the users's respiratory parameters as they may vary such as withrespect to activity. A range of values may be implemented as desired.For example, to estimate either “typical” or “elevated”characterizations of the user's respiratory parameters, higher values ofthe activity factor may be used in equation (3). In such an example, a“typical” inhalation flow profile may be obtained by setting theactivity factor to 1.25, and an “elevated” inhalation flow profilesuitable for active mode may be obtained by setting the activity factorto 2. The user's activity characterization may be entered or selected asinput to the oxygen concentrator 100 via the active mode button 630 orthe inactive mode button 635 on control panel 600 and the related valuemay be appropriately applied to the minimum alveolar minute ventilationdetermination.

A variant of equation (3) may include a further multiplying factor,PathologyFactor, which may take on different non-unity values associatedwith different pathologies, such as COPD, OHS, NMD, etc. The user'spathology may be entered as a manual setting to the oxygen concentrator100 via its control panel 600, and converted to a pathology factor, e.g.via a lookup table stored in the memory 420. For example, COPD may beassociated with a pathology factor of 1.25, with the result that theminimum, typical, and elevated estimates of alveolar minute ventilationwill be 25% greater than those of a healthy person.

3. Knowledge of breathing rate: Prior to therapy commencement, breathingrate may be initialized from determined and stored values from one ormore prior sessions or estimated from the user's height using populationdata. For example, FIG. 10A contains a graph 1000 illustrating a rangeof breathing rates for a range of heights from 50 to 180 centimetresderived from population age-rate data. The middle trace 1010 representsthe median breathing rate as a function of height. Thus, age and/orheight data may be entered or selected as input to the oxygenconcentrator 100 via its control panel 600 and the values may be appliedto a look-up table or function representing any of the curvesillustrated by the graph 1000 (e.g., median breathing rate at trace1010) for determination of breathing rate by the controller 400. Duringtherapy, step 830 may use POC sensor data, e.g. from the pressure sensor194, to estimate the user's breathing rate BR as described above.4. Estimation of minimum tidal volume: Step 820 estimates the user'sminimum tidal volume V_(T(min)) from the user's minimum alveolar minuteventilation, V^(&) _(ALV(min)), the user's breathing rate BR, and theanatomic deadspace VD_(an). For example, the controller 400 maydetermine minimum tidal volume V_(T(min)) by applying the followingequation:

$\begin{matrix}{V_{T(\min)} = {{VD_{an}} + \frac{{V\&}_{{ALV}(\min)}}{BR}}} & (4)\end{matrix}$

Optionally, the user's minimum minute ventilation may be estimated asthe product of the user's minimum tidal volume V_(T(min)) and the user'sbreathing rate BR, or as the sum of the product of the user's anatomicdeadspace VD_(an) and the user's breathing rate BR, and the user'sminimum alveolar minute ventilation, V^(&) _(ALV(min)).

5. Estimation of inspiratory time: The user's inspiratory time may beestimated from the pressure signal as described above. Step 840 in oneimplementation therefore processes data from the pressure sensor 194 toestimate the user's inspiratory time Ti as described above.

In an alternative implementation, step 840 uses published clinical datato obtain inspiratory time Ti from the user's height. For example, thecontroller 400 in step 840 may first obtain an estimate of breathingrate from user height by applying a function or look-up tablerepresenting data of the trace 1010 of the graph 1000 of FIG. 10A. Thecontroller 400 in step 840 may then apply a function or look-up tablerepresenting data in the curve 1060 in the graph 1050 in FIG. 10B(obtained from published clinical data) to obtain the inspiratory timeTi from the breath period (reciprocal of breathing rate in breaths persecond).

6. Estimation of the flow profile of the average inspiration: The shapeof the relative inhalation flow profile of a spontaneously breathinguser can be approximated by a template function q(t) that rises from 0to 1 and returns to 0 over the interval [0, 1]. The controller 400 mayfit this template function to a user's minimum tidal volume V_(T(min))and inspiratory time Ti to generate a minimum inhalation flow profileQ_(in(min))(t) for the user.

Step 860 therefore fits a template function q(t) to the minimum tidalvolume V_(T(min)) and inspiratory time Ti of the user to generate theuser's minimum inhalation flow profile Q_(in(min))(t), which takes theform

$Q_{peak}{q\left( \frac{t}{T_{I}} \right)}$

where Q_(peak) is the amplitude or peak value to be fitted. Step 860determines the peak flow rate Q_(peak) using the following definition oftidal volume:

$\begin{matrix}{V_{T(\min)} = {\int\limits_{0}^{T_{I}}{Q_{peak}{q\left( \frac{t}{T_{I}} \right)}{dt}}}} & (5)\end{matrix}$

In one implementation of step 860, the template function q(t) is asinusoidal half-wave (q(t)=sin(πt)), so the minimum inhalation flowprofile Q_(in(min))(t) takes the form of a sinusoidal half-wave of peakvalue Q_(peak) and duration equal to the inspiratory time Ti as follows:

$\begin{matrix}{{{Q_{{in}(\min)}(t)} = {Q_{peak}\sin\left( \frac{\pi t}{T_{I}} \right)}},{0 \leq t \leq T_{I}}} & (6)\end{matrix}$

The peak value Q_(peak) of the sinusoidal minimum inhalation flowprofile Q_(in(min))(t) is related to the minimum tidal volume V_(T(min))via the following formula:

$\begin{matrix}{Q_{peak} = {\frac{\pi}{2}\frac{{V_{T}}_{(\min)}}{T_{I}}}} & (7)\end{matrix}$

In other implementations, other template functions q(t) may be used togenerate the minimum inhalation flow profile Q_(in(min))(t), e.g. araised cosine (squared sine), parabola, root sine, or sine to the powerof 0.7. In such implementations there will be a different relationshipbetween the peak value Q_(peak) of the minimum inhalation flow profileand the minimum tidal volume V_(T(min)), derivable from equation (5).

7. Calculation of an alveolar time for the minimum sustainable tidalvolume: At step 870, the controller 400 uses the user's anatomicdeadspace VD_(an) estimated at step 810 and the minimum inhalation flowprofile Q_(in(min))(t) of the user generated at step 860 to calculatethe user's alveolar time T_(ALV). Step 870 uses the following relation:

$\begin{matrix}{{VD_{an}} = {\int_{T_{ALV}}^{T_{I}}{{Q_{{in}(\min)}(t)}{dt}}}} & (8)\end{matrix}$

8. Calculation of a delivery envelope: The delivery envelope isdetermined in accordance with the minimum inhalation flow profileQ_(in(min))(t) so that the bolus is bounded (e.g. in amplitude and time)by the onset of inhalation and the estimated alveolar time T_(ALV) asindicated by the profile.

For example, at step 880 the controller 400 derives the deliveryenvelope of the user based on the user's minimum inhalation flow profileQ_(in(min))(0 and the alveolar time T_(ALV) of the user. The deliveryenvelope is a set of constraints on the bolus parameters based on thealveolar time T_(ALV) calculated at step 870 and the minimum inhalationflow profile Q_(in(min))(t) calculated at step 860. The constraints areimposed by the avoidance of retrograde flow waste and anatomic deadspacewaste of the bolus volume. The constraints are:

$\begin{matrix}\begin{matrix}{{0 \leq {Q_{b}(t)} \leq {Q_{{in}(\min)}(t)}},} & {t \in \left\lbrack {t_{D},{t_{D} + t_{B}}} \right\rbrack} \\{{Q_{b}(t)} = 0} & {elsewhere}\end{matrix} & (9)\end{matrix}$ $\begin{matrix}{{t_{D} + t_{B}} \leq T_{ALV}} & (10)\end{matrix}$

where t_(D) is the onset delay of the bolus, t_(B) is the bolusduration, and Q_(b)(t) is the bolus amplitude profile. In some versions,one or more of the constraints (8, 9, 10) may be in the form ofprocessing rules for operation of the controller in relation tocontrolling bolus release as described in more detail herein.

Delivering POD Therapy Based on the Delivery Envelope

Once a delivery envelope is determined for a user, POD therapy may bedelivered to the user based on the delivery envelope. FIG. 9 contains aflow chart illustrating a method 900 for valve control over oxygenrelease that may be used to deliver the POD therapy. The method 900 maybe implemented by the controller 400, appropriately configured byprogram instructions stored in memory 420 or a carrier medium coupled tocontroller 400, and executed by one or more processors 410 as describedabove, for control of one or more supply valves (e.g., supply valve160).

The method 900 is represented as a loop, each iteration of whichcorresponds to a breath. The methods 800 and 900 may run substantiallyin parallel, so that the delivery envelope used by the method 900 isrepeatedly updated by the method 800 as the user's breathing rate andinspiratory time change.

The method 900 may start at step 910, which applies the breathing rateestimated at step 830 and one or more settings of the oxygenconcentrator 100 to determine a bolus volume for the POD therapy. Thedetermination at step 910 may implement a predetermined dose rationingscheme that sets out how the bolus volume varies with breathing rate andsettings of the oxygen concentrator 100, in particular the prescribedcontinuous flow rate set by the dosage buttons 620 to 626 on the controlpanel 600.

In one example of a dose rationing scheme, the bolus volume remainsfixed with breathing rate, but varies in proportion to the prescribedcontinuous flow rate set by the dosage buttons 620 to 626. As describedabove, in one implementation the bolus volume may be set to 11 mL foreach LPM of prescribed continuous flow rate. Fixed bolus volume schemestend to produce a more constant fraction of inspired oxygen (FiO₂) iftidal volume is approximately preserved as breathing rate changes.

In another example of a dose rationing scheme, the bolus volume isvaried in inverse proportion to the breathing rate, as well as inproportion to the prescribed continuous flow rate. So, for example, thebolus volume determined by step 910 at 40 BPM would be half the bolusvolume at 20 BPM for a given prescribed continuous flow rate. Under thisscheme, the average flow rate (minute volume) of oxygen remains fixedwith breathing rate. The oxygen delivered might not keep up withincreasing ventilation requirements, and users might expect to use ahigher continuous-flow-rate setting for exercise to avoid a drop inFiO₂.

Yet another example of a dose rationing scheme is a hybrid fixed bolusvolume/fixed minute volume scheme. Such a scheme may deliver fixed bolusvolumes at low breathing rates reverting to a fixed minute volume ofoxygen scheme when the maximum oxygen output (minute volume) of theoxygen concentrator 100 is reached.

In one implementation, the oxygen concentrator 100 may be configured toswitch from a fixed minute volume dose rationing scheme to a fixed bolusvolume dose rationing scheme, possibly with a higher bolus volume thancurrently being provided, on activation of a ‘boost’ control on thecontrol panel 600 of the oxygen concentrator 100. A user might activatesuch a control, for example, prior to commencing exercise. The oxygenconcentrator 100 may be configured to switch back from the fixed bolusvolume dose rationing scheme to the fixed minute volume dose rationingscheme either after a predetermined interval or on de-activation of the‘boost’ control. For example, in response to receiving a boost signalfrom an input interface (e.g., a boost button) of the oxygenconcentrator, the controller of the oxygen concentrator may controlrelease of one or more boost boluses. The total volume of oxygenenriched gas of each released boost bolus of the one or more boostboluses may include an equivalent volume that satisfies acontinuous-flow-rate setting of the oxygen concentrator as set at theinput interface plus an additional volume quantity of oxygen enrichedgas.

Step 920 follows, which uses the bolus volume calculated at step 910,the current delivery envelope as determined by the method 800, and(optionally) the POC sensor data to determine the bolus parameters. Oneor more implementations of step 920 are described below.

At the next step 930, the controller 400 awaits the onset of inhalation,which may be detected from the POC sensor data as described above.Finally, at step 940, the bolus is delivered according to the bolusparameters determined at step 920. The delivery of the bolus accordingto the bolus parameters is achieved by generating one or more bolusrelease control signals to actuate the supply valve 160 as describedabove, such as in accordance with timing and amplitude profile tosatisfy the determined delivery envelope.

The method 900 then returns to step 910 to calculate the volume of thebolus for the next breath.

In an alternative implementation, the bolus volume is only computedonce, so the method 900 returns to step 920 rather than step 910. In afurther alternative implementation, the bolus parameters are onlycomputed once, so the method 900 returns to step 930 rather than step910.

Determination of Bolus Parameters Based on the Delivery Envelope

In relation to the controller 400 generating a bolus release controlsignal at step 940 to achieve a given bolus volume V_(B), the bolusamplitude profile Q_(b)(t) must satisfy the volume constraint:

$\begin{matrix}{{\int\limits_{0}^{T_{I}}{{Q_{b}(t)}dt}} = V_{B}} & (11)\end{matrix}$

Any strategy to choose the onset delay t_(D), the bolus duration t_(B),and the bolus amplitude profile Q_(b)(t) within the delivery envelope(constraints (9) to (10)) and subject to the volume constraint (11) maybe used at step 920.

In one example, the bolus amplitude profile Q_(b)(t) follows the minimuminhalation flow profile Q_(in(min))(t) within the range [t_(D),t_(D)+t_(B)], and is zero outside that range, which satisfies constraint(9). An onset delay t_(D) may be chosen subject to constraint (10); thenapplying the volume constraint (11) fixes the bolus duration t_(B). Ifthe bolus duration t_(B) does not satisfy constraint (10), a lower onsetdelay t_(D) must be chosen and the process repeated until both the onsetdelay t_(D) and the bolus duration t_(B) satisfy constraint (10).Alternatively, a bolus duration t_(B) may be chosen subject toconstraint (10); then applying the volume constraint (11) fixes theonset delay t_(D). If the onset delay t_(D) does not satisfy constraint(10), a longer bolus duration t_(B) must be chosen and the processrepeated until both the onset delay t_(D) and the bolus duration t_(B)satisfy constraint (10).

In another example, the bolus amplitude profile Q_(b)(t) is constantwith a value of Q_(in(min))(t_(D)) within the range [t_(D),t_(D)+t_(B)], and zero outside that range, which satisfies constraint(9). A similar process to that described above of choosing an onsetdelay t_(D) subject to constraint (10) and applying the volumeconstraint (11) to fix the bolus duration t_(B), or vice versa, may befollowed.

In general, once the bolus amplitude profile Q_(b)(t) is chosen, thereis one degree of bolus timing freedom within the delivery envelope, i.e.the choice of bolus duration t_(B) determines the onset delay t_(D), orvice versa. The timing freedom is maximised if the bolus amplitude is ashigh as possible within the delivery envelope, which means bolusduration t_(B) is minimised. That degree of freedom may be utilised tooptimise the bolus timing over multiple breaths, so as to maximise thebeneficial effect of the bolus. Each successive iteration of step 920may choose a different bolus timing within the delivery envelope. Thebeneficial effect on the user of each bolus timing may be estimated,either subjectively by feedback from the user, via a user control on thecontrol panel 600, or objectively via a POC sensor that is connected tothe user (the optional input to step 920). One example of objectiveestimation is via an oxygen saturation sensor on the user's finger, witha larger value of oxygen saturation indicating a more beneficial effect.Another example of objective estimation may be via mainstream volumecapnography waveform analysis of the user's exhalate. This may allowinference of optimal timing for an oxygen bolus release duringinspiration. The capnogram's Phase 3 slope and fluctuations in slopethroughout exhalation provide coarse information on the efficiency ofgas exchange progressively within the lung, which may be informative (inreverse) during inspiration. FIG. 11 contains a graph 1100 showing threerepresentative volume capnograms (partial pressure of exhaled CO₂plotted against exhaled volume) from different user groups. Trace A isfrom healthy individuals, Trace B from an airway diseases group, andTrace C from an emphysema group. The different shapes, in particular theslope at the end of exhalation, indicate different dynamics of gasexchange throughout the breath. Similar information might be inferredusing sidestream capnogram monitoring, a technology suitable forincorporating into an oxygen concentrator such as the oxygenconcentrator 100.

By such measures, an optimisation strategy may guide the choice of bolustiming at the next iteration of step 920 so as to converge on a bolustiming that achieves the most beneficial effect. For example, suchfeedback may be implemented by the controller 400 to make incrementaladjustments to the bolus timing within the constraints previouslydescribed within a use session or over multiple use sessions so as toimprove the subjective feedback (e.g., user comfort) and/or objectivefeedback (saturation data). The controller 400 may then settle on abolus timing when such feedback obtains an optimum level. In thisfashion, the third kind of waste, physiologic deadspace waste, may beeffectively minimised, as the bolus timing that provides the mostbeneficial effect is the bolus timing that allows the bolus to reach thegreatest number of functioning alveoli, i.e. that minimises physiologicdeadspace waste.

Other considerations that may be implemented by a controller 400 insetting of bolus parameters within the delivery envelope may include:

-   -   User comfort: Discomfort within the nares may be associated with        an abruptly rising bolus. A softness setting via a user        ‘softness’ control may alter the initial rate of rise of bolus        amplitude, thereby affecting the duration of the bolus according        to the volume constraint (11).    -   Power consumption: if high delivery pressures invoke higher        power consumption, an ‘economy mode’ may be offered, such as        when operating from batteries, in which the bolus duration is        maximized such that delivery pressure and hence power        consumption are minimized.    -   Acoustic noise (e.g. operation during sleep or school): if lower        bolus amplitudes offer acoustic noise reduction, the bolus        duration may be maximised such that the bolus amplitude and        hence acoustic noise are minimised.

Other Applications of the Inhalation Flow Profile

Although the inhalation flow profile and the other user-size-derivedrespiratory parameter estimates described above have particular benefitsto oxygen concentrator POD therapy algorithms and system designoptimisation, they may also have application to respiratory therapiesother than PODs and respiratory therapy devices other than oxygenconcentrators. User-specific estimates of minimum, typical, or elevatedminute ventilation, tidal volume, anatomic deadspace, peak inspiratoryflow rate, and inhalation flow profile can assist pre-configuration orcontrol of a respiratory therapy device in a manner that is tailored tothe user. Some examples are:

-   -   Initialising tidal volume during volume control ventilation in        acute applications: It is recommended practice of modern acute        ventilation to minimize tidal volume (protective ventilation),        in order to reduce the possibility of ventilator-induced lung        injury. In doing so, minimising tidal volumes takes precedence        over normalising CO₂ (permissive hypercapnia). In this context        the use of a minimum tidal volume calculated from resting energy        expenditure/basal metabolic rate is well suited.    -   Initialising trigger sensitivity based on the minimum peak        inspiratory flow rate.    -   Initialising low or high tidal volume alarms based on the        minimum or elevated tidal volume respectively.    -   Initialising low or high minute ventilation alarms based on the        minimum or elevated minute ventilation respectively.    -   Initialising target tidal volume settings for volume assurance        modes using the typical tidal volume for a given pathology.    -   Assisting remote management of users on therapy, for instance        detection of hypoventilation using the minimum minute        ventilation.    -   Adapting internal behaviors of sophisticated ventilation        algorithms. For example:        -   When initiating users on nocturnal ventilation therapies, it            may be advantageous to reach the final therapy target            progressively, to permit the user to gradually acclimatize            to respiratory pressure therapy. The height-based minimum            ventilation estimates can determine a target minute            ventilation automatically, through knowledge of the user's            height, initial PaCO₂ and target PaCO₂. Thus, a device's            pressure support, volume or ventilation target can be            adjusted over multiple days or weeks to reach the final            clinical target for the therapy.        -   Automatic EPAP adjustment schemes typically respond to            hypopneas, usually judged relative to surrounding breaths. A            height-based minimum tidal volume estimate can be            implemented as an absolute reference, rather than just a            relative measure for judging hypopneas.

General Remarks

In the present disclosure, certain U.S. patents, U.S. patentapplications, and other materials (e.g., articles) have beenincorporated by reference. The text of such U.S. patents, U.S. patentapplications, and other materials is, however, only incorporated byreference to the extent that no conflict exists between such text andthe other statements and drawings set forth herein. In the event of suchconflict, then any such conflicting text in such incorporated byreference U.S. patents, U.S. patent applications, and other materials isspecifically not incorporated by reference in this patent.

Further modifications and alternative embodiments of various aspects ofthe invention may be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as embodiments. Elements and materials may besubstituted for those illustrated and described herein, parts andprocesses may be reversed, and certain features of the invention may beutilized independently, all as would be apparent to one skilled in theart after having the benefit of this description of the invention.Changes may be made in the elements described herein without departingfrom the spirit and scope of the invention as described in the followingclaims. For example, although the methodologies for valve control ofoxygen release are implemented in relation to a POC, they may also beimplemented with other devices, such as a high flow therapy device or arespiratory pressure therapy device (e.g., ventilator, CPAP or PAP) thatmay employ use of supplemental oxygen such with a POC or oxygen source.

Unless the context clearly dictates otherwise and where a range ofvalues is provided, it is understood that each intervening value, to thetenth of the unit of the lower limit, between the upper and lower limitof that range, and any other stated or intervening value in that statedrange is encompassed within the technology. The upper and lower limitsof these intervening ranges, which may be independently included in theintervening ranges, are also encompassed within the technology, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the technology.

Furthermore, where a value or values are stated herein as beingimplemented as part of the technology, it is understood that such valuesmay be approximated, unless otherwise stated, and such values may beutilized to any suitable significant digit to the extent that apractical technical implementation may permit or require it.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this technology belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present technology, a limitednumber of the exemplary methods and materials are described herein.

When a particular material is identified as being preferably used toconstruct a component, obvious alternative materials with similarproperties may be used as a substitute. Furthermore, unless specified tothe contrary, any and all components herein described are understood tobe capable of being manufactured and, as such, may be manufacturedtogether or separately.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include their plural equivalents,unless the context clearly dictates otherwise.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present technology isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates, which may need to be independently confirmed.

Moreover, in interpreting the disclosure, the terms “comprises” and“comprising” should be interpreted as referring to elements, components,or steps in a non-exclusive manner, indicating that the referencedelements, components, or steps may be present, or utilized, or combinedwith other elements, components, or steps that are not expresslyreferenced.

The subject headings used in the detailed description are included onlyfor the ease of reference of the reader and should not be used to limitthe subject matter found throughout the disclosure or the claims. Thesubject headings should not be used in construing the scope of theclaims or the claim limitations.

In some instances, the terminology and symbols may imply specificdetails that are not required to practice the technology. For example,although the terms “first” and “second” may be used, unless otherwisespecified, they are not intended to indicate any order but may beutilised to distinguish between distinct elements. Furthermore, althoughprocess steps in the methodologies may be described or illustrated in anorder, such an ordering is not required. Those skilled in the art willrecognize that such ordering may be modified and/or aspects thereof maybe conducted concurrently or even synchronously.

LABEL LIST

-   oxygen concentrator 100-   inlets 101-   air inlet 106-   inlet muffler 108-   accumulator 109-   valves 122-   valves 124-   concentrator outlet 130-   valves 132-   outlet muffler 133-   valves 134-   check valves 142-   check valves 144-   flow restrictors 151-   valves 152-   flow restrictors 153-   valve 154-   flow restrictors 155-   supply valve 160-   expansion chamber 162-   ultrasonic sensor system 165-   emitters 166-   receiver 168-   outer housing 170-   outlet 172-   outlet port 174-   small orifice flow restrictor 175-   power supply 180-   flow rate sensor 185-   filter 187-   connector 190-   conduit 192-   pressure sensor 194-   compression system 200-   compressor 210-   compressor outlet 212-   motor 220-   external armature 230-   air transfer device 240-   compressor outlet conduit 250-   canister system 300-   canister 302-   canister 304-   base 315-   outlet 325-   gases 327-   controller 400-   processor 410-   memory 420-   control panel 600-   input port 605-   power button 610-   button 620-   button 622-   button 624-   button 626-   button 630-   button 635-   altitude button 640-   battery check button 650-   relative battery power remaining LED 655-   graph 700-   airway delivery device 710-   trace 715-   mouthpiece 720-   trace 725-   trace 730-   amplitude 735-   onset delay 740-   inspiratory time 745-   duration 750-   potential waste 760-   interval 770-   method 800-   step 830-   step 840-   step 860-   step 870-   step 880-   method 900-   step 910-   step 920-   step 930-   step 940-   graph 1000-   trace 1010-   graph 1050-   curve 1060-   graph 1100

1. An oxygen concentrator apparatus comprising: at least two canisters;gas separation adsorbent disposed in the at least two canisters, whereinthe gas separation adsorbent separates at least some nitrogen from airin the at least two canisters to produce oxygen enriched gas; acompression system, the compression system comprising: a compressorcoupled to at least one of the canisters, wherein the compressorcompresses air during operation; and a motor coupled to the compressor,wherein the motor drives operation of the compressor; an accumulatorcoupled to one or more of the canisters, wherein oxygen enriched gasproduced in one or more of the canisters is passed into the accumulatorduring use; and a controller, including one or more processors, and aset of valves coupled to the controller, the controller configured tocontrol operation of the set of valves to (a) produce oxygen enrichedgas into the accumulator and (b) release the produced oxygen enrichedgas from the accumulator, the controller further configured to:determine one or more control parameters characterizing a deliverablebolus of oxygen enriched gas; generate a bolus release control signalfor controlling release of a bolus of oxygen enriched gas according tothe determined one or more control parameters; receive a boost signalfrom an input interface of the oxygen concentrator apparatus; and inresponse to the boost signal, control one or more further bolus releasecontrol signals for controlling release of one or more boost boluses,wherein a total volume of oxygen enriched gas of a released bolus of theone or more boost boluses includes: (1) an equivalent volume thatsatisfies a continuous-flow-rate setting of the oxygen concentratorapparatus as set at the input interface plus (2) an additional volumequantity of oxygen enriched gas.
 2. The oxygen concentrator apparatus ofclaim 1, wherein the controller is configured to discontinue release ofthe additional volume quantity of oxygen enriched gas after apredetermined time or in response to receiving a further signal from theinput interface of the oxygen concentrator apparatus.
 3. The oxygenconcentrator apparatus of claim 1 wherein the controller is furtherconfigured to: derive a delivery envelope of parameters of a potentialbolus of oxygen enriched gas; and determine the one or more controlparameters characterizing the deliverable bolus of oxygen enriched gasso that the one or more parameters are constrained within the deliveryenvelope.
 4. The oxygen concentrator apparatus of claim 3, wherein thecontroller is configured to derive the delivery envelope of parametersof the potential bolus of oxygen enriched gas using a size parameter ofa user.
 5. The oxygen concentrator apparatus of claim 4, wherein thecontroller is configured to receive the size parameter of the user. 6.The oxygen concentrator apparatus of claim 5, further comprising acontrol panel coupled to the controller and configured to receive thesize parameter of the user via manual entry.
 7. The oxygen concentratorapparatus of claim 1, wherein the oxygen concentrator apparatuscomprises a control panel coupled to the controller, and wherein theinput interface of the oxygen concentrator apparatus comprises thecontrol panel.
 8. A method of controlling oxygen enriched gas releasewith a controller of an oxygen concentrator in pulsed oxygen deliverymode, the method comprising: determining one or more control parameterscharacterizing a deliverable bolus of oxygen enriched gas; generating,with the controller, a bolus release control signal for controllingrelease of a bolus of oxygen enriched gas according to the determinedone or more control parameters; receiving, in the controller, a boostsignal from an input interface of the oxygen concentrator; and inresponse to the boost signal, controlling one or more further bolusrelease control signals for controlling release of one or more boostboluses, wherein a total volume of oxygen enriched gas of a releasedbolus of the one or more boost boluses includes: (1) an equivalentvolume that satisfies a continuous-flow-rate setting of the oxygenconcentrator as set at the input interface plus (2) an additional volumequantity of oxygen enriched gas.
 9. The method of claim 8, furthercomprising discontinuing, by the controller, release of the additionalvolume quantity of oxygen enriched gas after a predetermined time or inresponse to receiving, in the controller, a further signal from theinput interface of the oxygen concentrator.
 10. The method of claim 8further comprising: deriving a delivery envelope of parameters of apotential bolus of oxygen enriched gas; and determining the one or morecontrol parameters characterizing the deliverable bolus of oxygenenriched gas so that the one or more parameters are constrained withinthe delivery envelope.
 11. The method of claim 10, further comprisingderiving the delivery envelope of parameters of the potential bolus ofoxygen enriched gas using a size parameter of a user.
 12. The method ofclaim 11, further comprising, receiving, in the controller, the sizeparameter of the user.
 13. The method of claim 12, further comprisingreceiving the size parameter of the user via manual entry on a controlpanel coupled to the controller.
 14. The method of claim 8, wherein theinput interface of the oxygen concentrator comprises a control panelcoupled to the controller.
 15. An oxygen concentrator comprising acarrier medium having processor control instructions that, when executedby one or more processors of a controller of the oxygen concentrator,cause the oxygen concentrator to perform the method of claim 8.